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Prognostic markers of meningococcal disease in children: recent advances and future challenges Expert Rev. Anti Infect. Ther. 12(11), 1357–1369 (2014)
Marı´a Montero-Martı´n1–3, David P Inwald4, Enitan D Carrol5 and Federico Martino´n-Torres*1,2 1 Pediatric Infectious Disease and Vaccines Unit, A´rea Integrada de Pediatrı´a, Hospital Clı´nico Universitario de, Santiago de Compostela, A Choupana s.n., 15706 Santiago de Compostela, Spain 2 Genetics, Vaccines, Infections and Pediatrics Research Group (GENVIP), Healthcare Research Institute of Santiago de Compostela, Santiago de Compostela, A Choupana s.n, 15706 Santiago de Compostela, Spain 3 Department of Pediatrics, Hospital Universitario de Melilla, Remonta Street, Melilla 52006,, Spain 4 Paediatric Intensive Care Unit, St Mary’s Hospital, Imperial College Healthcare NHS Trust, Praed Street, London W2 1NY, UK 5 Department of Clinical Infection, Microbiology and Immunology, University of Liverpool Institute of Infection and Global Health, Ronald Ross Building, 8 West Derby Street, Liverpool L69 7BE, UK *Author for correspondence: Tel.: +34 981 950 615/610 Fax: +34 981 950 596 [email protected]
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Meningococcal disease is a life-threatening condition and a major cause of bacterial meningitis and sepsis worldwide. In many fatal cases, meningococcal disease is rapidly progressive and death occurs within hours of the initial symptoms. The early identification of patients at high risk of death would be useful in order to provide aggressive and more personalized clinical management with the proper level of supportive therapy required, contributing to an improvement in the survival rate and reduction in sequelae. The current study aims to review the current published literature about prognostic markers of meningococcal sepsis in children in order to elaborate conclusions and recommendations that could guide clinical practice and further research. KEYWORDS: children • marker • meningococcal • prognosis • score • sepsis • severity
Meningococcal disease is a life-threatening condition and a major cause of bacterial meningitis and sepsis worldwide. Meningococcal infection is caused by Neisseria meningitidis, an aerobic encapsulated Gram-negative diplococcus that can cause a wide variety of clinical presentations, ranging from subclinical infection to meningitis and fulminant sepsis [1]. Meningococci are classified based on capsular polysaccharides into 13 serogroups, with most disease cases currently being caused by serotypes A, B, C, Y and W135 [2]. Recent advances in preventive tools and the implementation of efficacious conjugate vaccines have achieved an important reduction in the incidence of this disease, especially in industrialized countries, although low-income settings continue to experience frequent and devastating outbreaks, especially sub-Saharan Africa, with an estimated 700,000 cases in the last 10 years according to WHO [3]. Furthermore, meningococcal disease remains to be an important cause of death and disability even in high-income countries, in spite of vaccination, technological improvement in diagnostic and therapeutic tools and the development
10.1586/14787210.2014.966079
of new antibiotic therapies [4]. Nowadays, the case fatality rate is about 10%, and up to 20% of patients with meningococcal disease will suffer from secondary complications, such as neurological defects, hearing loss or amputations of extremities or digits [5–7]. In most fatal cases, meningococcal disease is rapidly progressive and death occurs within hours of the initial symptoms. The early identification of patients at high risk of death or severe disease would be useful in order to provide aggressive and more personalized clinical management with the proper level of supportive therapy required, contributing to an improvement in the survival rate and reduction in sequelae. Therefore, a tool that could predict the evolution of meningococcal disease at an early stage would be of great clinical value and utility. Although there is currently not enough evidence to demonstrate that prognostic markers or severity scores improve the management or the outcome in children with meningococcal disease, several authors suggest that the use of severity scoring systems may help clinical management and also classification of patients for research purposes [8].
2014 Informa UK Ltd
ISSN 1478-7210
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´n-Torres Montero-Martı´n, Inwald, Carrol & Martino
It is well known that an ideal prognostic marker should be 100% sensitive, 100% specific, easy and quick to determine, objectively measurable, non-invasive, cheap and detectable at an early stage of the disease. This ideal represents a real challenge for the scientific community. In the last decades, innumerable investigations have been conducted to explore potential severity markers for meningococcal disease, ranging from laboratory parameters and clinical signs to genetic factors. Likewise, diverse prognostic scores have been developed and assessed, targeting to predict disease severity and mortality in both adults and children with meningococcal disease. The aim of this paper is to review the current published literature about prognostic markers of meningococcal sepsis in children in order to elaborate conclusions and recommendations that could guide clinical practice and further research. Methods
In this literature review, we conducted a thorough search of published studies about prognostic markers in children and young people with suspected or confirmed meningococcal disease. PUBMED, MEDLINE and DISCOVERY databases, Cochrane Library and the bibliographies of the most relevant studies were examined. The search was limited to studies published since January 2000 in English, French, Spanish and Portuguese. Randomized controlled trials, systematic reviews, meta-analysis, clinical guidelines, case–control studies and cohort studies were scrutinized to provide the strongest evidence. The search terms used were: (Meningococcal OR meningococcus) AND (sepsis OR disease OR infection) AND (children OR infant OR newborn OR neonate OR neonatal OR paediatric OR pediatric) AND (marker OR biomarker OR score OR scale) AND (prognostic OR prognosis OR severity). This search yielded 151 articles, but no randomized controlled trials. Papers were analyzed following the Critical Appraisal Skills Programme elaborated by the Oxford University Public Health Resources Unit. Findings Procalcitonin
Procalcitonin (PCT) is a pro-hormone of calcitonin but it is also an acute phase reactant with a short latency period of up to 6 h. Several authors have claimed that PCT may be a useful prognostic marker for meningococcal infection in children. Three independent prospective studies showed that a high PCT on admission in children with meningococcal disease was significantly associated with shock, multiorgan failure and death [9–11]. A prospective study of 65 children with confirmed meningococcal disease found that a PCT above 10 ng/ml was extremely sensitive for detecting patients at high risk of death (n = 9) or multiorgan dysfunction syndrome (n = 18), with 100% sensitivity in both cases. However, PCT had deficient specificity and positive predictive value (PPV), both below 50% [10]. Therefore, a PCT below 10 ng/ml in a child with 1358
meningococcal infection may be a useful predictor of good outcome [10]. Likewise, Hatherill et al. conducted another prospective observational study of 75 children with septic shock showed that PCT concentrations in the first 6 h after admission could help predict mortality in children with septic shock. This significant association was also documented when assessing the 37 included children with confirmed meningococcal etiology as an independent subcategory (mortality rate 4/37) [11]. These findings contrast with a British prospective observational study of 96 children with meningococcal sepsis [12]. A PCT on admission below 2 ng/ml was presented to be a good prognostic marker for septic shock, ventilation need and prolonged hospital stay (area under the curve = 0.85, 0.72 and 0.87, respectively), with a better performance than lactate and C-reactive protein. However, PCT was not significantly associated with death, possibly due to the lower mortality rate in the study series (only 5 patients died, mortality rate of 6%) compared with previous papers [12]. Hence, there is enough evidence to affirm that PCT is a useful biomarker for both identifying children with meningococcal infection and predicting disease severity and mortality in these patients. However, it must be noted that there is not a consensus about the ideal cutoff value of PCT for prognostic purposes, with different thresholds proposed by different authors. Further research is needed to investigate and clarify this issue. C-reactive protein
C-reactive protein (CRP) is an inflammatory marker that has been thoroughly investigated as an indicator of bacterial infection. It has poor specificity for differentiating bacterial infections from viral infections and a slow response time to bacterial proliferation, with a latency period of 6–12 h before levels start to increase [13,14]. The value of CRP as a severity marker in meningococcal sepsis is not well established. Some studies have shown an inverse association between CRP and mortality in children with meningococcal septic shock, suggesting it could be used as a severity predictor [15,16]. A retrospective study of 64 patients with meningococcal sepsis admitted to Pediatric Intensive Care Units (PICU) in the Netherlands showed that CRP levels at admission were significantly higher in non-survivors (n = 13) compared with survivors (n = 51), and importantly, two patients with meningococcal septic shock had CRP values within the normal range (1 survived and 1 died) [15]. By contrast, in a prospective study of 71 children with meningococcal disease, CRP was not associated with death (n = 14) or multiple organ failure (n = 21), but only significantly higher in patients with shock (n = 30, p = 0.008) [9]. Therefore, whether CRP could be used as a prognostic marker in meningococcal disease is not clear yet and further research will be needed to clarify its utility. Additionally, as commented previously for PCT, there is not a scientific agreement about the ideal threshold values of CRP as prognostic marker, which also needs to be investigated. Expert Rev. Anti Infect. Ther. 12(11), (2014)
Prognostic markers of meningococcal disease in children
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Full blood count parameters
Children with very severe infections often present with low white cell count, neutrophil count (NC) or platelet count. However, there is limited evidence about the value of full blood count parameters for diagnosing meningococcal disease in children presenting with fever and petechial rash, and for predicting severity or outcome in children with meningococcal disease [8]. A prospective observational study of 218 children with fever and petechial rash concluded that abnormal values in white cell count, NC or platelets were not good diagnostic markers for identifying children with meningococcal disease, as the specificity, sensitivity and predictive values were low [17]. When assessing the value of CRP to predict severity, a prospective observational study of 71 children with meningococcal disease suggested that a low NC on admission may be a good severity marker for meningococcal disease, being significantly associated with shock (n = 30), multiorgan dysfunction syndrome (n = 21) and death (n = 14) [9]. When considering white blood cells (WBC), a Chilean prospective study of 75 children with meningococcal disease showed that a WBC below 5000/mm3 on admission was significantly associated with death (n = 5). However, although the sensitivity and NPV of this threshold were 100%, the specificity and PPV were limited (88 and 38%, respectively) [18]. On the other hand, a multicenter study of 216 children with confirmed meningococcal disease admitted to PICU in the USA questions the value of WBC and NC as severity markers, stating that the sensitivity and NPV of these markers are notably suboptimal [19]. Nevertheless, this paper has important limitations, such as the retrospective study design and the exclusion of 17% of participants due to unavailability of differential counts. Summarizing, the value of blood count parameters as severity markers of meningococcal disease is currently controversial and further research may be useful to clarify their role. Coagulation parameters
It is well known that altered fibrinolysis and anti-coagulation factors are involved in the pathophysiology of meningococcal sepsis and play an important role in the promotion of severity and mortality. Actually, children with severe disease often present with a marked coagulopathy. Therefore, it is reasonable to think that some of these factors may be used as severity markers for meningococcal sepsis. Some authors have shown that high levels of the plasminogen activator inhibitor 1 (PAI-1) may be positively associated with mortality [20,21]. Likewise, low levels of plasminogen and a2-antiplasmin, and high concentrations of plasmin–antiplasmin complexes may be useful markers of severe meningococcal disease, disseminated intravascular coagulation (DIC) and shock [20]. It is also known that children with severe and fulminant meningococcal disease have low levels of natural anticoagulant factors, such as protein C and antithrombin [22,23]. In our literature review, we only found one recent study evaluating the value of clotting factors as predictive markers of informahealthcare.com
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meningococcal sepsis. A prospective study of 112 children with severe meningococcal sepsis admitted to PICU indicated that thrombin activatable fibrinolysis inhibitor (TAFI), TAFI activation peptide (TAFI-AP) and inactivated TAFI [TAFIa(i)] may be good severity markers for meningococcal sepsis in children [24]. TAFI levels on admission were inversely associated with shock (n = 96) and normalized during the convalescence phase. TAFI-AP concentrations were positively associated with DIC (n = 76) and death (n = 12), while TAFIa(i) was significantly associated with death, but not with DIC [24]. However, further investigations are necessary to demonstrate the utility of TAFI, TAFI-AP and TAFIa(i) as prognostic markers of meningococcal sepsis in children. Adrenocorticotropic hormone & cortisol
It is widely known that the hypothalamic–pituitary–adrenal axis is involved in the regulation of the inflammatory response, which is crucial in the course of severe infections. Some patients with meningococcal disease develop adrenal insufficiency secondary to hemorrhagic injury and usually have a torpid and even fatal course [25]. In 2001, two prospective observational studies in the Netherlands investigated the role of the hormones in the hypothalamic–pituitary–adrenal axis as prognostic markers of meningococcal disease in children admitted to PICU [26,27]. Woensel et al. studied 32 children with meningococcal disease, of which 10 had distinct meningococcal meningitis, 10 had both meningococcal meningitis and septic shock and 12 patients suffered fulminant septic shock. They found that patients with fulminant septic shock had significantly higher levels of adrenocorticotropic hormone (ACTH) on admission and lower levels of cortisol than children without shock [27]. Cortisol levels were inversely associated with some proinflammatory mediators, such as IL-6, IL-8 and IL-10 [27]. Kleijn et al. included 72 children with meningococcal sepsis and found that low cortisol levels and high ACTH concentrations were significantly associated with death (16.7% reported mortality rate) [26]. Therefore, determining cortisol levels and ACTH concentrations on admission may be potentially useful in identifying children with meningococcal disease at a high risk of severe disease or death, but further research is needed to confirm these findings. Lipopolysaccharide & cholesterol
Lipopolysaccharide (LPS) is a component of the external membrane of N. meningitidis, which is released to the bloodstream during infection and acts as an endotoxin, triggering the systemic inflammatory response of the host. LPS induces the production of TNF and IL-6. High LPS blood levels are correlated with disease severity and outcome in meningococcal sepsis [28]. Cholesterol and lipoproteins are involved in clearance of LPS by creating neutralizing complexes and therefore may play an important role in the host defensive response against meningococcal infection [29,30]. 1359
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However, there is little evidence about the utility of lipoproteins and cholesterol as prognostic markers of meningococcal sepsis in children. A retrospective study in the Netherlands quantified total cholesterol level, low-density lipoprotein and high-density lipoprotein serum levels in 57 children with meningococcal sepsis or septic shock [31]. Disease severity was assessed with severity scores, such as the Pediatric Risk of Mortality Score (PRISM), and the reported mortality was 17.5%. The authors found exceptionally low concentrations of total serum cholesterol and lipoproteins on admission in all enrolled children, being inversely associated with illness severity. Only total cholesterol concentrations were significantly associated with death [31]. In survivors, lipoproteins and total cholesterol levels started to upsurge 24 h after PICU admission with total normalization 1–3 months afterward. Interestingly, there was a positive correlation between total cholesterol and cortisol levels, which nearly reached statistical significance (p = 0.054) [32]. Cholesterol is an essential substrate in the production of cortisol and hypocholesterolemia may probably contribute to a deficient adrenal response to meningococcal disease and therefore to a poorer prognosis. Further studies with a more robust design and larger sample size are needed to confirm these associations and investigate the potential clinical utility of cholesterol and lipoprotein levels as severity markers in meningococcal disease in children. Cytokines & chemokines
It is widely known that a complex network of markers and mediators are secreted and released in meningococcal disease in response to the detection of certain components of N. meningitidis, such as LPS and some proteins of the meningococcal external membrane. Chemokines and cytokines, as part of this rich communication system, play an important role in the pathophysiology of meningococcal disease, especially in meningococcal sepsis, and could be used as potential prognostic markers [11,25,32]. TNF is an essential cytokine in the modulation of inflammation and has been widely studied and suggested to be a good severity marker [11]. A prospective study of 75 children with septic shock showed that TNF levels on admission were positively associated with death and multiple organ failure [11]. On the receiver operating characteristic curve, TNF levels were a more accurate severity predictor than PCT or IL-10, but not as good as the PRISM [11]. The same paper also explored the role of IL-10, showing that high levels on admission were also significantly associated with death, but not with multiorgan dysfunction syndrome [11]. It must be mentioned that authors used the multiple organ system failure score to identify patients with multiorgan dysfunction syndrome, but they did not specify how many study participants had this outcome. Likewise, it must be noted that the observed mortality rate of 28% (21/75) is substantially higher than the average reported in other papers [5]. In 2006, a retrospective observational study of 58 children with clinical meningococcal sepsis conducted in the Netherlands 1360
investigated the serum levels of monocyte chemoattractant protein (MCP)-1, macrophage inflammatory protein (MIP)-1a, growth-related gene product (GRO)-a and IL-8 on admission and 24 h later [32]. Fifty-two patients had septic shock and nine died. All chemokines concentrations were markedly high on admission, with a significant decrease at 24 h. Serum concentrations of MCP-1, MIP-1a, GRO-a, IL-8, IL-6 and TNF-a were significantly higher in patients with septic shock versus patients with sepsis, and in non-survivors compared with survivors [32]. Importantly, MCP-1, MIP-1a, GRO-a, IL-8 and IL-6 were better prognostic markers than TNF-a, with a similar specificity (94–98 vs 98%, respectively) and a better sensitivity (100 vs 78%, respectively) [32]. Interestingly, Carrol et al. concluded after a prospective observational study of 63 children with confirmed meningococcal disease, that an anti-inflammatory cytokine profile could be associated with severe disease and septic shock [33]. They found that high IL-1Ra/TNF and IL-1Ra/IL-6 were significantly associated with severe disease and septic shock, compared with non-severe meningococcal disease [33]. However, they found no significant difference in cytokine profiles between survivors and non-survivors. In this study, a patient was considered having severe disease when the Glasgow Meningococcal Septicaemia Prognostic Score (GMSPS) was equal or above 8. Thirty-six participants had severe disease, 21 suffered from septic shock and 9 died. The importance of alterations in the pro/anti-inflammatory profile was also reported by Sprong et al. regarding an observational retrospective study of 111 children who had survived an episode of severe meningococcal disease [34]. Patients were stratified into four groups according to disease severity and clinical manifestations: bacteremia (n = 24), meningitis (n = 33), shock plus meningitis (n = 11) or shock (n = 43). They found that a reduced production capacity of IL-1b and a low IL-1b/ IL-10 ratio was significantly associated with disease severity. However, the production capacity of other cytokines, such as TNF, IL-12 and IL-10, were not related to disease severity [34]. It must be noted that the present study has a selection bias, as only surviving patients were included, which could affect its external validity. The median delay between admission to hospital and participation in the study was 5 years. The findings of both studies suggest that the ratio of proand anti-inflammatory cytokines may be more relevant than individual values when predicting disease severity and outcome in pediatric meningococcal disease. Therefore, instead of investigating single cytokines as biomarkers, further research should concentrate on exploring cytokine profiles, which may have a greater potential as severity indicators in meningococcal disease. Nevertheless, it must be highlighted that the determination of cytokine and chemokine levels is not currently available as rapid bedside tests and hence, their clinical utility as prognostic markers is likely to be limited. Intestinal fatty acid binding protein
Intestinal fatty acid binding protein (I-FABP) is a small protein present in the cytosol of mature enterocytes and it is released Expert Rev. Anti Infect. Ther. 12(11), (2014)
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to the bloodstream in response to mucosal damage [35,36]. I-FABP blood levels are very low in healthy subjects, but increase significantly when there is gut mucosal injury, with a good correlation with the severity of splanchnic ischemia in adults [37]. A recent retrospective study conducted in the Netherlands investigated I-FABP role as a prognostic marker in meningococcal disease. Nineteen patients with meningococcal sepsis admitted to PICU were included and three patients died. The results suggested that I-FABP may be a good severity marker in children with meningococcal sepsis, arguing that the blood flow redistribution to vital structures can cause splanchnic hypoperfusion in critically ill children [38]. Persistently high levels of I-FABP in the first 12 h after admission were significantly associated with death. Moreover, I-FABP levels on admission correlated well with other severity markers, such as the Rotterdam Score, the PRISM II and IL-6 [38]. However, this study has important limitations, such as the small sample size and the retrospective study design, so further research is needed to confirm these findings and clarify the role of I-FABP as a severity marker of meningococcal sepsis in children.
Review
homozygote children for this polymorphism (4G/4G) have been reported to present the highest PAI-1 levels and are even more prone to suffer from DIC, multiorgan failure and vascular sequelae [41–43]. This paper included 27 case–control studies with 7245 patients, reporting an overall mortality rate of 10%. Therefore, the current evidence suggests that this polymorphism in SERPINE1 may be a valuable prognostic marker in children with meningococcal disease. If these findings are confirmed, analyzing SERPINE1 gene could be of important clinical utility Personalized adjunctive treatments could be developed and administered to patients with high-risk polymorphisms. For example, activated protein C can reduce PAI-1 levels by forming 1:1 complexes, stimulating fibrinolysis and thus, may potentially improve prognosis in patients with SERPINE polymorphism [44]. Some authors have suggested a positive effect of adjunctive therapy with activated protein C concentrates in patients with severe sepsis [45,46]. Further research would be needed to investigate the utility of therapy with activated protein C in patients with invasive meningococcal disease and high-risk SERPINE1 polymorphisms. Fc receptors of immunoglobulins
Genetic markers
In the last decades, many studies have investigated the genetic basis of meningococcal disease, searching for genetic factors associated with both disease susceptibility and severity. Very diverse factors have been explored, scrutinizing the different stages of the pathophysiology of meningococcal disease. To date, numerous authors have studied genetic determinants related to various coagulation factors, cytokines, mucous membrane immunity, innate immunity and acquired immunity responses, mitochondrial DNA and angiotensin-converting enzyme [39]. Recent population-based studies have identified genetic mutations and single nucleotide polymorphisms (SNP) that could be associated with both disease susceptibility and severity. The most promising findings are related to coagulation and the acquired and innate immune systems, in particular to the PAI-1, the Fc receptors of immunoglobulins (FcR), the Tolllike receptors (TLR) and the complement factor H (CFH). This paper focuses on disease severity rather than susceptibility. Plasminogen activator inhibitor 1
PAI-1 is a glycoprotein that inhibits the fibrinolysis cascade by inhibiting the tissue plasminogen activator. Some studies suggest that high levels of PAI-1 may be associated with a higher risk of death in children with meningococcal disease [20,21]. PAI-1 has been widely investigated from the genetic point of view, searching for mutations or polymorphisms that could be associated with susceptibility, disease severity or outcome in meningococcal disease. A recent systematic review and metaanalysis has confirmed that a functional polymorphism in SERPINE1 (the promoting region of PAI-1 coding gene) is associated with higher production of PAI-1 and confers a significant higher risk of DIC and death [40]. Interestingly, informahealthcare.com
The receptors of the Fc fraction of immunoglobulins are located in the outer membrane of phagocytes and are essential for an effective phagocytosis. Three subtypes are involved in the host immune response against N. meningitidis: FcgRIIa, FcgRIIIa and FcgRIIIb. Several studies have explored whether FcR polymorphisms could be associated with disease susceptibility and severity in meningococcal disease. There is promising evidence suggesting that specific Fc allotypes may be associated with disease severity in established meningococcal disease. A Spanish observational study of 145 adults with confirmed meningococcal disease and 290 healthy controls found that the FcgRIIIa-R/R131 allotype was associated with a significantly higher risk of complications and sequelae in those with disease [47]. However, the distribution of allotypes was similar between healthy controls and patients, suggesting that the FcgRIIIa-R/R131 allotype may be a prognostic marker of meningococcal disease, but not involved in susceptibility to the disease [47]. Disease severity was assessed using a prognostic score designed by the Barcelona Meningococcal Disease Surveillance Group [48]. Toll-like receptors
TLRs are transmembrane pattern recognition receptors that recognize specific molecular structures of microorganisms, such as external membrane porins (TLR2), LPS (TLR4) or bacterial DNA patterns (TLR9). Once identified, a biochemical cascade is triggered and proinflammatory cytokines and chemokines produced and released to the bloodstream. A recent multicenter prospective study investigated the role of TLR4 as prognostic marker of meningococcal disease. One hundred and ninety-seven European Caucasian children with MD were included and TLR4 genotyped. Genetic polymorphisms 1361
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were correlated with death and disease severity, evaluated by the need for ventilation, inotropic support, skin graft and/or limb/digit amputation [49]. Overall mortality was 9.6%. TLR4 Asp299Gly polymorphism appeared to be significantly associated with death in all ages (odds ratio [OR]: 3.3; 95% CI: 1.14–9.73) and especially in children under 2 years old (OR: 6.6; 95% CI: 1.7–25.6). The same polymorphism was only significantly associated with need for ventilation support in children under 2 (OR: 9.2; 95% CI: 2.2–38.5), but not with skin grafting or limb/digit loss [49]. Furthermore, TLRs other than TLR4 have also been investigated as potential prognostic markers. A recent retrospective study conducted in the Netherlands explored the role the role of TLR9 SNP as prognostic markers in children with meningococcal meningitis (MM) [50]. They included 390 survivors to MM and evaluated the association of TLR9 SNPs with other severity markers of MM. TLR9 +2848 and –1237 polymorphisms were significantly associated with higher leucocyte count in cerebrospinal fluid (CSF), lower CSF/blood glucose ratio and lower probability of positive blood culture. No TLR9 SNPs were associated with PICU admission, sepsis, hearing loss, academic or behavioral problems [50]. The authors suggest that TLR9 +2848 and –1237 polymorphisms may confer a better bactericidal immune response against meningococcus in CSF. The clinical utility of these findings is probably limited and we must be cautious when interpreting these results due to the potential selection and information bias affecting this study. Moreover, another recent paper investigated the role of SNPs in TLR2, 4 and 9 as prognostic markers of disease severity and clinical outcome in children with bacterial meningitis [51]. They included 393 survivors of bacterial meningitis: 327 children with MM and 66 with pneumococcal meningitis. TLR4 +896 polymorphism was significantly associated with hearing loss, particularly in MM (OR: 7.6; 95% CI: 2.3–24). The risk for hearing loss was also higher in combined carrier of TLR4 +896 and TLR9 –1237, with an OR of 4.3 for MM (95% CI: 1.3–14.2). No association was found between TLR SNPs and other variables related to disease severity or clinical outcome (CSF parameters, CRP, blood culture results, convulsions, consciousness level, convulsions, sepsis and PICU admission) [51]. Once more, these findings must be cautiously interpreted, having in mind the limitations and potential bias due to the study design. In conclusion, TLR4 Asp299Gly polymorphism might be a useful prognostic marker in MD, especially in children under 2, but further research is needed. Likewise, there not enough evidence to support the role of TLR4 +896 and TLR9 – 1237 as predictors for hearing loss in MM in children. Complement factors
The complement system is a crucial element of the host immune response against bacterial infections. It is activated through three different pathways: the classical pathway, the MBL pathway and the alternative pathway. They all converge in the activation of the C3 converting enzyme, which triggers 1362
the destruction of the pathogen by stimulating the chemotaxis of macrophages and neutrophils, the opsonization and phagocytosis of antigens and the direct lysis of bacterial membranes [52]. The complement factor H is involved in the activation of the alternative pathway. It has been reported that both the deficiency and the hyperexpression of CFH are associated with a higher susceptibility of meningococcal disease [53–55]. No published studies have associated CFH polymorphisms or mutations with disease severity, outcome or sequelae in meningococcal disease. Consequently, specific polymorphisms of CFH gene might be useful markers to identify children with a special vulnerability to invasive meningococcal infection, but not as prognostic markers in those who already have meningococcal disease. Composite scores
In the last decades, multiple scores have been developed in order to assess disease severity in children with infectious conditions and try to predict their clinical evolution over time. Very diverse scores have been used to evaluate children with meningococcal disease, ranging from generic scores for critically ill children, such as the PRISM and the multiple organ system failure score, to specific scales, especially designed to assess patients with meningococcal infection, such as the GMSPS and the Rotterdam score. In the current review, we will comment the most recent and relevant studies about well-established severity scales and newly developed scores. Pediatric risk of mortality score
The PRISM is a generic scale designed to assess disease severity and predict the risk of death in critically ill children admitted to PICU, regardless of the cause of admission [56]. It is calculated using 14 variables and 23 subvariables, with both clinical and laboratory parameters. It requires the observation of the patient for at least 8–12 h, ideally 24 h, which is an important limitation. PRISM has been proven to be a good score for identifying children at high risk of death and severe disease, including patients with meningococcal disease [57]. However, PRISM was not designed to evaluate children with meningococcal disease, so it is reasonable to think that it may disregard disease-specific prognostic factors. A Brazilian prospective study of 49 children with confirmed meningococcal sepsis admitted to PICU showed that PRISM score ‡11 was significantly associated with death (mortality rate 18%) and well correlated with the GMSPS score [58]. Moreover, Blanco-Quiro´s et al. published that PRISM was a good predictor of mortality (n = 14), shock (n = 30) and multiorgan failure (n = 21) in children with meningococcal disease [9]. A retrospective multicenter study of 192 children with meningococcal septic shock admitted to PICU showed that PRISM II was useful to discriminate between survivors and non-survivors, with a similar discriminative capability than Expert Rev. Anti Infect. Ther. 12(11), (2014)
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GMSPS score and better than other specific scales, such as Leclerc and Gedde-Dahl’s scores [59]. It must be noted that this study reports a mortality rate of 34%, which is far higher than the average mortality in developed countries [5].
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Glasgow Meningococcal Septicaemia Prognostic Score
GMSPS is a scale especially designed to evaluate children with meningococcal sepsis and predict the risk of death [60,61]. It ranges from 0 to 15 points and is mainly based on clinical parameters, with only one laboratory variable which is not even essential. It has important clinical advantages, as it is simple, easy and quick to calculate. GMSPS has been retrospectively and prospectively validated and proven to have a good performance in the early identification of patients at high risk of mortality and sequelae [60,61]. It is currently recommended by the most recent British and Spanish clinical guidelines as reference severity score for children with meningococcal sepsis [8,62]. A prospective multicenter cohort study of 278 children with meningococcal disease in the UK investigated the performance of GMSPS in comparison with other 9 severity scores and laboratory markers [60]. One hundred and one participants presented with septicemia, 151 with meningitis plus septicemia and 26 with definite meningitis. Twenty-six participants died (9.4%). A GMSPS score ‡8 on admission had a 79% sensitivity and 86% specificity for predicting death, improving to 100% sensitivity if calculated in the first 12 h. It was well correlated with other severity scores (Stokland, Stiehm and Damrosch, Ansari, Niklasson, Leclerc, Kahn and Blum, Lewis, Istanbul and Bjark) and laboratory parameters (endotoxin, IL-6, IL-10, TNF-a) and appeared to have good reproducibility [60]. Other studies previously commented have suggested a similar utility to PRISM score in predicting mortality, shock and multiple organ failure in children with meningococcal disease [9,58,59]. However, GMSPS also has some notable limitations. It is not wholly objective, as it mainly relies on clinical assessment and some score elements are especially subjective or difficult to determine, such as the assessment of ‘the deterioration of the patient in the last hour’ or the ‘skin/rectal temperature difference’. Moreover, GMSPS has not been updated or reviewed since its development in the 90s, despite the great improvement in prognosis of meningococcal disease brought by therapeutic advances in the last decades. BEP score: base excess & platelet count
The base excess and platelet count (BEP) score is a new score designed to predict mortality in children with meningococcal sepsis [63]. It is calculated from two objective laboratory parameters, base excess and platelet count, which can be quick and objectively measurable at presentation. It has been recently validated in a multicenter cohort study in 1073 European children with meningococcal sepsis admitted to PICU [63]. Eighty-five participants died, with a reported mortality rate of 7.9%. In this study, BEP score appeared to have a good performance in detecting children at high risk of death, with high sensitivity informahealthcare.com
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and specificity, similar to Rotterdam score, but inferior to PRISM [63]. However, this study has an important limitation, as the time of sample collection is not clearly defined, which may affect the validity of the results. Therefore, the BEP score is a promising score, but further research is needed to investigate its evolution over the first 24 h of presentation, to determinate the best time-point for sample collection, and to validate it in non-European populations. Platelets & neutrophils product
The platelets and neutrophils (PN) product is a relatively new score designed to identify patients with meningococcal disease at high risk of death [64]. It was developed and validated by Peters et al. in a prospective multicenter study of 227 patients with meningococcal disease admitted to PICU in the UK [64]. It is calculated multiplying the platelet and neutrophil count at the time of admission to hospital, which confers the advantages of been objectively measurable and ready at an early stage. Peters et al. claimed that the PN product may be a useful prognostic score, with a better performance than platelet count or NC independently and other severity scales, such as the GMSPS. They reported a 73% sensitivity, 99% specificity and 82% PPV to predict death for a PN product of
Review
Prognostic markers of meningococcal disease in children: recent advances and future challenges Expert Rev. Anti Infect. Ther. 12(11), 1357–1369 (2014)
Marı´a Montero-Martı´n1–3, David P Inwald4, Enitan D Carrol5 and Federico Martino´n-Torres*1,2 1 Pediatric Infectious Disease and Vaccines Unit, A´rea Integrada de Pediatrı´a, Hospital Clı´nico Universitario de, Santiago de Compostela, A Choupana s.n., 15706 Santiago de Compostela, Spain 2 Genetics, Vaccines, Infections and Pediatrics Research Group (GENVIP), Healthcare Research Institute of Santiago de Compostela, Santiago de Compostela, A Choupana s.n, 15706 Santiago de Compostela, Spain 3 Department of Pediatrics, Hospital Universitario de Melilla, Remonta Street, Melilla 52006,, Spain 4 Paediatric Intensive Care Unit, St Mary’s Hospital, Imperial College Healthcare NHS Trust, Praed Street, London W2 1NY, UK 5 Department of Clinical Infection, Microbiology and Immunology, University of Liverpool Institute of Infection and Global Health, Ronald Ross Building, 8 West Derby Street, Liverpool L69 7BE, UK *Author for correspondence: Tel.: +34 981 950 615/610 Fax: +34 981 950 596 [email protected]
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Meningococcal disease is a life-threatening condition and a major cause of bacterial meningitis and sepsis worldwide. In many fatal cases, meningococcal disease is rapidly progressive and death occurs within hours of the initial symptoms. The early identification of patients at high risk of death would be useful in order to provide aggressive and more personalized clinical management with the proper level of supportive therapy required, contributing to an improvement in the survival rate and reduction in sequelae. The current study aims to review the current published literature about prognostic markers of meningococcal sepsis in children in order to elaborate conclusions and recommendations that could guide clinical practice and further research. KEYWORDS: children • marker • meningococcal • prognosis • score • sepsis • severity
Meningococcal disease is a life-threatening condition and a major cause of bacterial meningitis and sepsis worldwide. Meningococcal infection is caused by Neisseria meningitidis, an aerobic encapsulated Gram-negative diplococcus that can cause a wide variety of clinical presentations, ranging from subclinical infection to meningitis and fulminant sepsis [1]. Meningococci are classified based on capsular polysaccharides into 13 serogroups, with most disease cases currently being caused by serotypes A, B, C, Y and W135 [2]. Recent advances in preventive tools and the implementation of efficacious conjugate vaccines have achieved an important reduction in the incidence of this disease, especially in industrialized countries, although low-income settings continue to experience frequent and devastating outbreaks, especially sub-Saharan Africa, with an estimated 700,000 cases in the last 10 years according to WHO [3]. Furthermore, meningococcal disease remains to be an important cause of death and disability even in high-income countries, in spite of vaccination, technological improvement in diagnostic and therapeutic tools and the development
10.1586/14787210.2014.966079
of new antibiotic therapies [4]. Nowadays, the case fatality rate is about 10%, and up to 20% of patients with meningococcal disease will suffer from secondary complications, such as neurological defects, hearing loss or amputations of extremities or digits [5–7]. In most fatal cases, meningococcal disease is rapidly progressive and death occurs within hours of the initial symptoms. The early identification of patients at high risk of death or severe disease would be useful in order to provide aggressive and more personalized clinical management with the proper level of supportive therapy required, contributing to an improvement in the survival rate and reduction in sequelae. Therefore, a tool that could predict the evolution of meningococcal disease at an early stage would be of great clinical value and utility. Although there is currently not enough evidence to demonstrate that prognostic markers or severity scores improve the management or the outcome in children with meningococcal disease, several authors suggest that the use of severity scoring systems may help clinical management and also classification of patients for research purposes [8].
2014 Informa UK Ltd
ISSN 1478-7210
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It is well known that an ideal prognostic marker should be 100% sensitive, 100% specific, easy and quick to determine, objectively measurable, non-invasive, cheap and detectable at an early stage of the disease. This ideal represents a real challenge for the scientific community. In the last decades, innumerable investigations have been conducted to explore potential severity markers for meningococcal disease, ranging from laboratory parameters and clinical signs to genetic factors. Likewise, diverse prognostic scores have been developed and assessed, targeting to predict disease severity and mortality in both adults and children with meningococcal disease. The aim of this paper is to review the current published literature about prognostic markers of meningococcal sepsis in children in order to elaborate conclusions and recommendations that could guide clinical practice and further research. Methods
In this literature review, we conducted a thorough search of published studies about prognostic markers in children and young people with suspected or confirmed meningococcal disease. PUBMED, MEDLINE and DISCOVERY databases, Cochrane Library and the bibliographies of the most relevant studies were examined. The search was limited to studies published since January 2000 in English, French, Spanish and Portuguese. Randomized controlled trials, systematic reviews, meta-analysis, clinical guidelines, case–control studies and cohort studies were scrutinized to provide the strongest evidence. The search terms used were: (Meningococcal OR meningococcus) AND (sepsis OR disease OR infection) AND (children OR infant OR newborn OR neonate OR neonatal OR paediatric OR pediatric) AND (marker OR biomarker OR score OR scale) AND (prognostic OR prognosis OR severity). This search yielded 151 articles, but no randomized controlled trials. Papers were analyzed following the Critical Appraisal Skills Programme elaborated by the Oxford University Public Health Resources Unit. Findings Procalcitonin
Procalcitonin (PCT) is a pro-hormone of calcitonin but it is also an acute phase reactant with a short latency period of up to 6 h. Several authors have claimed that PCT may be a useful prognostic marker for meningococcal infection in children. Three independent prospective studies showed that a high PCT on admission in children with meningococcal disease was significantly associated with shock, multiorgan failure and death [9–11]. A prospective study of 65 children with confirmed meningococcal disease found that a PCT above 10 ng/ml was extremely sensitive for detecting patients at high risk of death (n = 9) or multiorgan dysfunction syndrome (n = 18), with 100% sensitivity in both cases. However, PCT had deficient specificity and positive predictive value (PPV), both below 50% [10]. Therefore, a PCT below 10 ng/ml in a child with 1358
meningococcal infection may be a useful predictor of good outcome [10]. Likewise, Hatherill et al. conducted another prospective observational study of 75 children with septic shock showed that PCT concentrations in the first 6 h after admission could help predict mortality in children with septic shock. This significant association was also documented when assessing the 37 included children with confirmed meningococcal etiology as an independent subcategory (mortality rate 4/37) [11]. These findings contrast with a British prospective observational study of 96 children with meningococcal sepsis [12]. A PCT on admission below 2 ng/ml was presented to be a good prognostic marker for septic shock, ventilation need and prolonged hospital stay (area under the curve = 0.85, 0.72 and 0.87, respectively), with a better performance than lactate and C-reactive protein. However, PCT was not significantly associated with death, possibly due to the lower mortality rate in the study series (only 5 patients died, mortality rate of 6%) compared with previous papers [12]. Hence, there is enough evidence to affirm that PCT is a useful biomarker for both identifying children with meningococcal infection and predicting disease severity and mortality in these patients. However, it must be noted that there is not a consensus about the ideal cutoff value of PCT for prognostic purposes, with different thresholds proposed by different authors. Further research is needed to investigate and clarify this issue. C-reactive protein
C-reactive protein (CRP) is an inflammatory marker that has been thoroughly investigated as an indicator of bacterial infection. It has poor specificity for differentiating bacterial infections from viral infections and a slow response time to bacterial proliferation, with a latency period of 6–12 h before levels start to increase [13,14]. The value of CRP as a severity marker in meningococcal sepsis is not well established. Some studies have shown an inverse association between CRP and mortality in children with meningococcal septic shock, suggesting it could be used as a severity predictor [15,16]. A retrospective study of 64 patients with meningococcal sepsis admitted to Pediatric Intensive Care Units (PICU) in the Netherlands showed that CRP levels at admission were significantly higher in non-survivors (n = 13) compared with survivors (n = 51), and importantly, two patients with meningococcal septic shock had CRP values within the normal range (1 survived and 1 died) [15]. By contrast, in a prospective study of 71 children with meningococcal disease, CRP was not associated with death (n = 14) or multiple organ failure (n = 21), but only significantly higher in patients with shock (n = 30, p = 0.008) [9]. Therefore, whether CRP could be used as a prognostic marker in meningococcal disease is not clear yet and further research will be needed to clarify its utility. Additionally, as commented previously for PCT, there is not a scientific agreement about the ideal threshold values of CRP as prognostic marker, which also needs to be investigated. Expert Rev. Anti Infect. Ther. 12(11), (2014)
Prognostic markers of meningococcal disease in children
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Full blood count parameters
Children with very severe infections often present with low white cell count, neutrophil count (NC) or platelet count. However, there is limited evidence about the value of full blood count parameters for diagnosing meningococcal disease in children presenting with fever and petechial rash, and for predicting severity or outcome in children with meningococcal disease [8]. A prospective observational study of 218 children with fever and petechial rash concluded that abnormal values in white cell count, NC or platelets were not good diagnostic markers for identifying children with meningococcal disease, as the specificity, sensitivity and predictive values were low [17]. When assessing the value of CRP to predict severity, a prospective observational study of 71 children with meningococcal disease suggested that a low NC on admission may be a good severity marker for meningococcal disease, being significantly associated with shock (n = 30), multiorgan dysfunction syndrome (n = 21) and death (n = 14) [9]. When considering white blood cells (WBC), a Chilean prospective study of 75 children with meningococcal disease showed that a WBC below 5000/mm3 on admission was significantly associated with death (n = 5). However, although the sensitivity and NPV of this threshold were 100%, the specificity and PPV were limited (88 and 38%, respectively) [18]. On the other hand, a multicenter study of 216 children with confirmed meningococcal disease admitted to PICU in the USA questions the value of WBC and NC as severity markers, stating that the sensitivity and NPV of these markers are notably suboptimal [19]. Nevertheless, this paper has important limitations, such as the retrospective study design and the exclusion of 17% of participants due to unavailability of differential counts. Summarizing, the value of blood count parameters as severity markers of meningococcal disease is currently controversial and further research may be useful to clarify their role. Coagulation parameters
It is well known that altered fibrinolysis and anti-coagulation factors are involved in the pathophysiology of meningococcal sepsis and play an important role in the promotion of severity and mortality. Actually, children with severe disease often present with a marked coagulopathy. Therefore, it is reasonable to think that some of these factors may be used as severity markers for meningococcal sepsis. Some authors have shown that high levels of the plasminogen activator inhibitor 1 (PAI-1) may be positively associated with mortality [20,21]. Likewise, low levels of plasminogen and a2-antiplasmin, and high concentrations of plasmin–antiplasmin complexes may be useful markers of severe meningococcal disease, disseminated intravascular coagulation (DIC) and shock [20]. It is also known that children with severe and fulminant meningococcal disease have low levels of natural anticoagulant factors, such as protein C and antithrombin [22,23]. In our literature review, we only found one recent study evaluating the value of clotting factors as predictive markers of informahealthcare.com
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meningococcal sepsis. A prospective study of 112 children with severe meningococcal sepsis admitted to PICU indicated that thrombin activatable fibrinolysis inhibitor (TAFI), TAFI activation peptide (TAFI-AP) and inactivated TAFI [TAFIa(i)] may be good severity markers for meningococcal sepsis in children [24]. TAFI levels on admission were inversely associated with shock (n = 96) and normalized during the convalescence phase. TAFI-AP concentrations were positively associated with DIC (n = 76) and death (n = 12), while TAFIa(i) was significantly associated with death, but not with DIC [24]. However, further investigations are necessary to demonstrate the utility of TAFI, TAFI-AP and TAFIa(i) as prognostic markers of meningococcal sepsis in children. Adrenocorticotropic hormone & cortisol
It is widely known that the hypothalamic–pituitary–adrenal axis is involved in the regulation of the inflammatory response, which is crucial in the course of severe infections. Some patients with meningococcal disease develop adrenal insufficiency secondary to hemorrhagic injury and usually have a torpid and even fatal course [25]. In 2001, two prospective observational studies in the Netherlands investigated the role of the hormones in the hypothalamic–pituitary–adrenal axis as prognostic markers of meningococcal disease in children admitted to PICU [26,27]. Woensel et al. studied 32 children with meningococcal disease, of which 10 had distinct meningococcal meningitis, 10 had both meningococcal meningitis and septic shock and 12 patients suffered fulminant septic shock. They found that patients with fulminant septic shock had significantly higher levels of adrenocorticotropic hormone (ACTH) on admission and lower levels of cortisol than children without shock [27]. Cortisol levels were inversely associated with some proinflammatory mediators, such as IL-6, IL-8 and IL-10 [27]. Kleijn et al. included 72 children with meningococcal sepsis and found that low cortisol levels and high ACTH concentrations were significantly associated with death (16.7% reported mortality rate) [26]. Therefore, determining cortisol levels and ACTH concentrations on admission may be potentially useful in identifying children with meningococcal disease at a high risk of severe disease or death, but further research is needed to confirm these findings. Lipopolysaccharide & cholesterol
Lipopolysaccharide (LPS) is a component of the external membrane of N. meningitidis, which is released to the bloodstream during infection and acts as an endotoxin, triggering the systemic inflammatory response of the host. LPS induces the production of TNF and IL-6. High LPS blood levels are correlated with disease severity and outcome in meningococcal sepsis [28]. Cholesterol and lipoproteins are involved in clearance of LPS by creating neutralizing complexes and therefore may play an important role in the host defensive response against meningococcal infection [29,30]. 1359
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However, there is little evidence about the utility of lipoproteins and cholesterol as prognostic markers of meningococcal sepsis in children. A retrospective study in the Netherlands quantified total cholesterol level, low-density lipoprotein and high-density lipoprotein serum levels in 57 children with meningococcal sepsis or septic shock [31]. Disease severity was assessed with severity scores, such as the Pediatric Risk of Mortality Score (PRISM), and the reported mortality was 17.5%. The authors found exceptionally low concentrations of total serum cholesterol and lipoproteins on admission in all enrolled children, being inversely associated with illness severity. Only total cholesterol concentrations were significantly associated with death [31]. In survivors, lipoproteins and total cholesterol levels started to upsurge 24 h after PICU admission with total normalization 1–3 months afterward. Interestingly, there was a positive correlation between total cholesterol and cortisol levels, which nearly reached statistical significance (p = 0.054) [32]. Cholesterol is an essential substrate in the production of cortisol and hypocholesterolemia may probably contribute to a deficient adrenal response to meningococcal disease and therefore to a poorer prognosis. Further studies with a more robust design and larger sample size are needed to confirm these associations and investigate the potential clinical utility of cholesterol and lipoprotein levels as severity markers in meningococcal disease in children. Cytokines & chemokines
It is widely known that a complex network of markers and mediators are secreted and released in meningococcal disease in response to the detection of certain components of N. meningitidis, such as LPS and some proteins of the meningococcal external membrane. Chemokines and cytokines, as part of this rich communication system, play an important role in the pathophysiology of meningococcal disease, especially in meningococcal sepsis, and could be used as potential prognostic markers [11,25,32]. TNF is an essential cytokine in the modulation of inflammation and has been widely studied and suggested to be a good severity marker [11]. A prospective study of 75 children with septic shock showed that TNF levels on admission were positively associated with death and multiple organ failure [11]. On the receiver operating characteristic curve, TNF levels were a more accurate severity predictor than PCT or IL-10, but not as good as the PRISM [11]. The same paper also explored the role of IL-10, showing that high levels on admission were also significantly associated with death, but not with multiorgan dysfunction syndrome [11]. It must be mentioned that authors used the multiple organ system failure score to identify patients with multiorgan dysfunction syndrome, but they did not specify how many study participants had this outcome. Likewise, it must be noted that the observed mortality rate of 28% (21/75) is substantially higher than the average reported in other papers [5]. In 2006, a retrospective observational study of 58 children with clinical meningococcal sepsis conducted in the Netherlands 1360
investigated the serum levels of monocyte chemoattractant protein (MCP)-1, macrophage inflammatory protein (MIP)-1a, growth-related gene product (GRO)-a and IL-8 on admission and 24 h later [32]. Fifty-two patients had septic shock and nine died. All chemokines concentrations were markedly high on admission, with a significant decrease at 24 h. Serum concentrations of MCP-1, MIP-1a, GRO-a, IL-8, IL-6 and TNF-a were significantly higher in patients with septic shock versus patients with sepsis, and in non-survivors compared with survivors [32]. Importantly, MCP-1, MIP-1a, GRO-a, IL-8 and IL-6 were better prognostic markers than TNF-a, with a similar specificity (94–98 vs 98%, respectively) and a better sensitivity (100 vs 78%, respectively) [32]. Interestingly, Carrol et al. concluded after a prospective observational study of 63 children with confirmed meningococcal disease, that an anti-inflammatory cytokine profile could be associated with severe disease and septic shock [33]. They found that high IL-1Ra/TNF and IL-1Ra/IL-6 were significantly associated with severe disease and septic shock, compared with non-severe meningococcal disease [33]. However, they found no significant difference in cytokine profiles between survivors and non-survivors. In this study, a patient was considered having severe disease when the Glasgow Meningococcal Septicaemia Prognostic Score (GMSPS) was equal or above 8. Thirty-six participants had severe disease, 21 suffered from septic shock and 9 died. The importance of alterations in the pro/anti-inflammatory profile was also reported by Sprong et al. regarding an observational retrospective study of 111 children who had survived an episode of severe meningococcal disease [34]. Patients were stratified into four groups according to disease severity and clinical manifestations: bacteremia (n = 24), meningitis (n = 33), shock plus meningitis (n = 11) or shock (n = 43). They found that a reduced production capacity of IL-1b and a low IL-1b/ IL-10 ratio was significantly associated with disease severity. However, the production capacity of other cytokines, such as TNF, IL-12 and IL-10, were not related to disease severity [34]. It must be noted that the present study has a selection bias, as only surviving patients were included, which could affect its external validity. The median delay between admission to hospital and participation in the study was 5 years. The findings of both studies suggest that the ratio of proand anti-inflammatory cytokines may be more relevant than individual values when predicting disease severity and outcome in pediatric meningococcal disease. Therefore, instead of investigating single cytokines as biomarkers, further research should concentrate on exploring cytokine profiles, which may have a greater potential as severity indicators in meningococcal disease. Nevertheless, it must be highlighted that the determination of cytokine and chemokine levels is not currently available as rapid bedside tests and hence, their clinical utility as prognostic markers is likely to be limited. Intestinal fatty acid binding protein
Intestinal fatty acid binding protein (I-FABP) is a small protein present in the cytosol of mature enterocytes and it is released Expert Rev. Anti Infect. Ther. 12(11), (2014)
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to the bloodstream in response to mucosal damage [35,36]. I-FABP blood levels are very low in healthy subjects, but increase significantly when there is gut mucosal injury, with a good correlation with the severity of splanchnic ischemia in adults [37]. A recent retrospective study conducted in the Netherlands investigated I-FABP role as a prognostic marker in meningococcal disease. Nineteen patients with meningococcal sepsis admitted to PICU were included and three patients died. The results suggested that I-FABP may be a good severity marker in children with meningococcal sepsis, arguing that the blood flow redistribution to vital structures can cause splanchnic hypoperfusion in critically ill children [38]. Persistently high levels of I-FABP in the first 12 h after admission were significantly associated with death. Moreover, I-FABP levels on admission correlated well with other severity markers, such as the Rotterdam Score, the PRISM II and IL-6 [38]. However, this study has important limitations, such as the small sample size and the retrospective study design, so further research is needed to confirm these findings and clarify the role of I-FABP as a severity marker of meningococcal sepsis in children.
Review
homozygote children for this polymorphism (4G/4G) have been reported to present the highest PAI-1 levels and are even more prone to suffer from DIC, multiorgan failure and vascular sequelae [41–43]. This paper included 27 case–control studies with 7245 patients, reporting an overall mortality rate of 10%. Therefore, the current evidence suggests that this polymorphism in SERPINE1 may be a valuable prognostic marker in children with meningococcal disease. If these findings are confirmed, analyzing SERPINE1 gene could be of important clinical utility Personalized adjunctive treatments could be developed and administered to patients with high-risk polymorphisms. For example, activated protein C can reduce PAI-1 levels by forming 1:1 complexes, stimulating fibrinolysis and thus, may potentially improve prognosis in patients with SERPINE polymorphism [44]. Some authors have suggested a positive effect of adjunctive therapy with activated protein C concentrates in patients with severe sepsis [45,46]. Further research would be needed to investigate the utility of therapy with activated protein C in patients with invasive meningococcal disease and high-risk SERPINE1 polymorphisms. Fc receptors of immunoglobulins
Genetic markers
In the last decades, many studies have investigated the genetic basis of meningococcal disease, searching for genetic factors associated with both disease susceptibility and severity. Very diverse factors have been explored, scrutinizing the different stages of the pathophysiology of meningococcal disease. To date, numerous authors have studied genetic determinants related to various coagulation factors, cytokines, mucous membrane immunity, innate immunity and acquired immunity responses, mitochondrial DNA and angiotensin-converting enzyme [39]. Recent population-based studies have identified genetic mutations and single nucleotide polymorphisms (SNP) that could be associated with both disease susceptibility and severity. The most promising findings are related to coagulation and the acquired and innate immune systems, in particular to the PAI-1, the Fc receptors of immunoglobulins (FcR), the Tolllike receptors (TLR) and the complement factor H (CFH). This paper focuses on disease severity rather than susceptibility. Plasminogen activator inhibitor 1
PAI-1 is a glycoprotein that inhibits the fibrinolysis cascade by inhibiting the tissue plasminogen activator. Some studies suggest that high levels of PAI-1 may be associated with a higher risk of death in children with meningococcal disease [20,21]. PAI-1 has been widely investigated from the genetic point of view, searching for mutations or polymorphisms that could be associated with susceptibility, disease severity or outcome in meningococcal disease. A recent systematic review and metaanalysis has confirmed that a functional polymorphism in SERPINE1 (the promoting region of PAI-1 coding gene) is associated with higher production of PAI-1 and confers a significant higher risk of DIC and death [40]. Interestingly, informahealthcare.com
The receptors of the Fc fraction of immunoglobulins are located in the outer membrane of phagocytes and are essential for an effective phagocytosis. Three subtypes are involved in the host immune response against N. meningitidis: FcgRIIa, FcgRIIIa and FcgRIIIb. Several studies have explored whether FcR polymorphisms could be associated with disease susceptibility and severity in meningococcal disease. There is promising evidence suggesting that specific Fc allotypes may be associated with disease severity in established meningococcal disease. A Spanish observational study of 145 adults with confirmed meningococcal disease and 290 healthy controls found that the FcgRIIIa-R/R131 allotype was associated with a significantly higher risk of complications and sequelae in those with disease [47]. However, the distribution of allotypes was similar between healthy controls and patients, suggesting that the FcgRIIIa-R/R131 allotype may be a prognostic marker of meningococcal disease, but not involved in susceptibility to the disease [47]. Disease severity was assessed using a prognostic score designed by the Barcelona Meningococcal Disease Surveillance Group [48]. Toll-like receptors
TLRs are transmembrane pattern recognition receptors that recognize specific molecular structures of microorganisms, such as external membrane porins (TLR2), LPS (TLR4) or bacterial DNA patterns (TLR9). Once identified, a biochemical cascade is triggered and proinflammatory cytokines and chemokines produced and released to the bloodstream. A recent multicenter prospective study investigated the role of TLR4 as prognostic marker of meningococcal disease. One hundred and ninety-seven European Caucasian children with MD were included and TLR4 genotyped. Genetic polymorphisms 1361
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were correlated with death and disease severity, evaluated by the need for ventilation, inotropic support, skin graft and/or limb/digit amputation [49]. Overall mortality was 9.6%. TLR4 Asp299Gly polymorphism appeared to be significantly associated with death in all ages (odds ratio [OR]: 3.3; 95% CI: 1.14–9.73) and especially in children under 2 years old (OR: 6.6; 95% CI: 1.7–25.6). The same polymorphism was only significantly associated with need for ventilation support in children under 2 (OR: 9.2; 95% CI: 2.2–38.5), but not with skin grafting or limb/digit loss [49]. Furthermore, TLRs other than TLR4 have also been investigated as potential prognostic markers. A recent retrospective study conducted in the Netherlands explored the role the role of TLR9 SNP as prognostic markers in children with meningococcal meningitis (MM) [50]. They included 390 survivors to MM and evaluated the association of TLR9 SNPs with other severity markers of MM. TLR9 +2848 and –1237 polymorphisms were significantly associated with higher leucocyte count in cerebrospinal fluid (CSF), lower CSF/blood glucose ratio and lower probability of positive blood culture. No TLR9 SNPs were associated with PICU admission, sepsis, hearing loss, academic or behavioral problems [50]. The authors suggest that TLR9 +2848 and –1237 polymorphisms may confer a better bactericidal immune response against meningococcus in CSF. The clinical utility of these findings is probably limited and we must be cautious when interpreting these results due to the potential selection and information bias affecting this study. Moreover, another recent paper investigated the role of SNPs in TLR2, 4 and 9 as prognostic markers of disease severity and clinical outcome in children with bacterial meningitis [51]. They included 393 survivors of bacterial meningitis: 327 children with MM and 66 with pneumococcal meningitis. TLR4 +896 polymorphism was significantly associated with hearing loss, particularly in MM (OR: 7.6; 95% CI: 2.3–24). The risk for hearing loss was also higher in combined carrier of TLR4 +896 and TLR9 –1237, with an OR of 4.3 for MM (95% CI: 1.3–14.2). No association was found between TLR SNPs and other variables related to disease severity or clinical outcome (CSF parameters, CRP, blood culture results, convulsions, consciousness level, convulsions, sepsis and PICU admission) [51]. Once more, these findings must be cautiously interpreted, having in mind the limitations and potential bias due to the study design. In conclusion, TLR4 Asp299Gly polymorphism might be a useful prognostic marker in MD, especially in children under 2, but further research is needed. Likewise, there not enough evidence to support the role of TLR4 +896 and TLR9 – 1237 as predictors for hearing loss in MM in children. Complement factors
The complement system is a crucial element of the host immune response against bacterial infections. It is activated through three different pathways: the classical pathway, the MBL pathway and the alternative pathway. They all converge in the activation of the C3 converting enzyme, which triggers 1362
the destruction of the pathogen by stimulating the chemotaxis of macrophages and neutrophils, the opsonization and phagocytosis of antigens and the direct lysis of bacterial membranes [52]. The complement factor H is involved in the activation of the alternative pathway. It has been reported that both the deficiency and the hyperexpression of CFH are associated with a higher susceptibility of meningococcal disease [53–55]. No published studies have associated CFH polymorphisms or mutations with disease severity, outcome or sequelae in meningococcal disease. Consequently, specific polymorphisms of CFH gene might be useful markers to identify children with a special vulnerability to invasive meningococcal infection, but not as prognostic markers in those who already have meningococcal disease. Composite scores
In the last decades, multiple scores have been developed in order to assess disease severity in children with infectious conditions and try to predict their clinical evolution over time. Very diverse scores have been used to evaluate children with meningococcal disease, ranging from generic scores for critically ill children, such as the PRISM and the multiple organ system failure score, to specific scales, especially designed to assess patients with meningococcal infection, such as the GMSPS and the Rotterdam score. In the current review, we will comment the most recent and relevant studies about well-established severity scales and newly developed scores. Pediatric risk of mortality score
The PRISM is a generic scale designed to assess disease severity and predict the risk of death in critically ill children admitted to PICU, regardless of the cause of admission [56]. It is calculated using 14 variables and 23 subvariables, with both clinical and laboratory parameters. It requires the observation of the patient for at least 8–12 h, ideally 24 h, which is an important limitation. PRISM has been proven to be a good score for identifying children at high risk of death and severe disease, including patients with meningococcal disease [57]. However, PRISM was not designed to evaluate children with meningococcal disease, so it is reasonable to think that it may disregard disease-specific prognostic factors. A Brazilian prospective study of 49 children with confirmed meningococcal sepsis admitted to PICU showed that PRISM score ‡11 was significantly associated with death (mortality rate 18%) and well correlated with the GMSPS score [58]. Moreover, Blanco-Quiro´s et al. published that PRISM was a good predictor of mortality (n = 14), shock (n = 30) and multiorgan failure (n = 21) in children with meningococcal disease [9]. A retrospective multicenter study of 192 children with meningococcal septic shock admitted to PICU showed that PRISM II was useful to discriminate between survivors and non-survivors, with a similar discriminative capability than Expert Rev. Anti Infect. Ther. 12(11), (2014)
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GMSPS score and better than other specific scales, such as Leclerc and Gedde-Dahl’s scores [59]. It must be noted that this study reports a mortality rate of 34%, which is far higher than the average mortality in developed countries [5].
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Glasgow Meningococcal Septicaemia Prognostic Score
GMSPS is a scale especially designed to evaluate children with meningococcal sepsis and predict the risk of death [60,61]. It ranges from 0 to 15 points and is mainly based on clinical parameters, with only one laboratory variable which is not even essential. It has important clinical advantages, as it is simple, easy and quick to calculate. GMSPS has been retrospectively and prospectively validated and proven to have a good performance in the early identification of patients at high risk of mortality and sequelae [60,61]. It is currently recommended by the most recent British and Spanish clinical guidelines as reference severity score for children with meningococcal sepsis [8,62]. A prospective multicenter cohort study of 278 children with meningococcal disease in the UK investigated the performance of GMSPS in comparison with other 9 severity scores and laboratory markers [60]. One hundred and one participants presented with septicemia, 151 with meningitis plus septicemia and 26 with definite meningitis. Twenty-six participants died (9.4%). A GMSPS score ‡8 on admission had a 79% sensitivity and 86% specificity for predicting death, improving to 100% sensitivity if calculated in the first 12 h. It was well correlated with other severity scores (Stokland, Stiehm and Damrosch, Ansari, Niklasson, Leclerc, Kahn and Blum, Lewis, Istanbul and Bjark) and laboratory parameters (endotoxin, IL-6, IL-10, TNF-a) and appeared to have good reproducibility [60]. Other studies previously commented have suggested a similar utility to PRISM score in predicting mortality, shock and multiple organ failure in children with meningococcal disease [9,58,59]. However, GMSPS also has some notable limitations. It is not wholly objective, as it mainly relies on clinical assessment and some score elements are especially subjective or difficult to determine, such as the assessment of ‘the deterioration of the patient in the last hour’ or the ‘skin/rectal temperature difference’. Moreover, GMSPS has not been updated or reviewed since its development in the 90s, despite the great improvement in prognosis of meningococcal disease brought by therapeutic advances in the last decades. BEP score: base excess & platelet count
The base excess and platelet count (BEP) score is a new score designed to predict mortality in children with meningococcal sepsis [63]. It is calculated from two objective laboratory parameters, base excess and platelet count, which can be quick and objectively measurable at presentation. It has been recently validated in a multicenter cohort study in 1073 European children with meningococcal sepsis admitted to PICU [63]. Eighty-five participants died, with a reported mortality rate of 7.9%. In this study, BEP score appeared to have a good performance in detecting children at high risk of death, with high sensitivity informahealthcare.com
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and specificity, similar to Rotterdam score, but inferior to PRISM [63]. However, this study has an important limitation, as the time of sample collection is not clearly defined, which may affect the validity of the results. Therefore, the BEP score is a promising score, but further research is needed to investigate its evolution over the first 24 h of presentation, to determinate the best time-point for sample collection, and to validate it in non-European populations. Platelets & neutrophils product
The platelets and neutrophils (PN) product is a relatively new score designed to identify patients with meningococcal disease at high risk of death [64]. It was developed and validated by Peters et al. in a prospective multicenter study of 227 patients with meningococcal disease admitted to PICU in the UK [64]. It is calculated multiplying the platelet and neutrophil count at the time of admission to hospital, which confers the advantages of been objectively measurable and ready at an early stage. Peters et al. claimed that the PN product may be a useful prognostic score, with a better performance than platelet count or NC independently and other severity scales, such as the GMSPS. They reported a 73% sensitivity, 99% specificity and 82% PPV to predict death for a PN product of
