Article

Laboratory parameters for predicting Salmonella bacteraemia: a prospective cohort study

Tropical Doctor 0(0) 1–4 ! The Author(s) 2017 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0049475517734118 journals.sagepub.com/home/tdo

Suhendro Suwarto1, Hadianti Adlani2, Leonard Nainggolan3, Cleopas Martin Rumende4 and Amin Soebandrio5,6

Abstract Blood cultures for a definitive diagnosis of typhoid fever takes time and are not routinely available. We thus investigated laboratory parameters to predict Salmonella bacteraemia. We conducted a prospective cohort study in Jakarta, Indonesia. Patients with suspected typhoid fever admitted to hospital from October 2014 to December 2016 were included. Out of 187 individuals, 27 had Salmonella typhi and 12 had S. paratyphi in blood cultures. Absolute eosinopenia, elevated aspartate aminotransferase and elevated C-reactive protein > 40 mg/L were positive predictors.

Keywords Aspartate aminotransferase (AST), blood culture, C-reactive protein (CRP), eosinopenia, Salmonella, typhoid fever

Background

Methods

Typhoid fever is transmitted to humans by food or water contaminated with Salmonella enterica serotype Typhi or Paratyphi.1 It is endemic in several Asian countries, including Indonesia,2 and is the third commonest cause for hospital admission and is a serious community health.3 Clinically, typhoid presents with acute fever—particularly at night, relative bradycardia, constipation, coated tongue, hepatomegaly and/or splenomegaly.4–6 Routine laboratory parameters, including leukopenia, absolute eosinopenia, thrombocytopenia, elevated serum levels of aspartate aminotransferase (AST) and alanine transaminase (ALT), have been reported to be helpful in establishing the diagnosis.6,7 Serological tests, such as the Widal test, are commonly used in low-income countries, as these are inexpensive and easy to perform.8,9 Furthermore, increased serum levels of CRP > 40 mg/L indicate serious inflammation.10 A previous report suggested that this alone could be used to diagnose enteric fever.11 However, despite these purported associations, a definitive diagnosis requires isolation of S. typhi and/or S. paratyphi in blood cultures,12,13 even though the sensitivity of such detection has been reported to be only 40%.14 Furthermore, microbial blood culture as the gold standard is not available universally and requires considerable time and cost.13

Ours was a prospective cohort study conducted in two public and three private hospitals in JakartaTangerang, Indonesia, between October 2014 and December 2016. Patients who were aged 14 years or older with clinically suspected typhoid fever were 1 Senior Lecturer, Division of Tropical and Infectious Diseases, Department of Internal Medicine, Faculty of Medicine Universitas Indonesia, Dr. Cipto Mangunkusumo National General Hospital, Jakarta, Indonesia 2 Associate Lecturer, Department of Internal Medicine, Faculty of Medicine Universitas Indonesia, Dr. Cipto Mangunkusumo National General Hospital, Jakarta, Indonesia 3 Lecturer, Division of Tropical and Infectious Diseases, Department of Internal Medicine, Faculty of Medicine Universitas Indonesia, Dr. Cipto Mangunkusumo National General Hospital, Jakarta, Indonesia 4 Senior Lecturer, Department of Internal Medicine, Faculty of Medicine Universitas Indonesia, Dr. Cipto Mangunkusumo National General Hospital, Jakarta, Indonesia 5 Professor, Eijkman Institute for Molecular Biology, Jakarta, Indonesia 5 Professor, Department of Microbiology, Faculty of Medicine Universitas Indonesia, Jakarta, Indonesia

Corresponding author: Suhendro Suwarto, Division of Tropical and Infectious Diseases, Department of Internal Medicine, Faculty of Medicine, Universitas Indonesia, Dr. Cipto Mangunkusumo National General Hospital (RSCM), Jl. Diponegoro No. 71, Jakarta Pusat 10430, Jakarta, Indonesia. Email: [email protected]

2 included after informed consent was obtained. Typhoid was suspected in patients presenting with an acute fever for >4 days with an axillary temperature of 38.0 C accompanied by at least one of the following clinical signs: evening fever; constipation; coated tongue; relative bradycardia; hepatomegaly; or splenomegaly. Those with chronic liver disease and/or pregnancy were excluded. Clinical findings and laboratory parameters were recorded after patients were admitted through the emergency room. The following were recorded for each patient: leucocyte, eosinophil and platelet counts; levels of liver transaminases; CRP levels; and Widal test results. One set of blood samples was obtained from each patient upon admission in the emergency room. Samples were classified as positive for Salmonella when S. typhi or S. paratyphi were detected in cultures within five days. Blood cultures for Salmonella were performed using the BD BACTECTM (Becton Dickinson and Company, Sparks, NV, USA) automated microbiology blood culture system, according to manufacturers’ instructions. Any sample that was found to be positive was removed and subjected to Gram stain analysis. Negative cultures were reinserted into the incubator. Cultures were considered negative if no growth was detected after five days. Confirmed positive cultures were subjected to further identification and antimicrobial susceptibility testing using the VITEKÕ 2 Compact instrument (bioMerieux, France) (http://www.biomerieux-diagnostics.com/vitek-2-compact). The sample size of this study was calculated based on a minimum of  20 events per variable, with a total number of variables of seven. Thus, the minimum sample size required was 140 patients.15 The 2 test was used to test for differences between the seven independent categorical variables and dependent variables (positive or negative for Salmonella). All independent predictors that were significantly associated with the dependent variables were then subjected to logistic regression analysis. The Hosmer–Lemeshow test was used to analyse goodness of fit of the model, and the receiver operating characteristic (ROC) was assessed for its discrimination. STATA software version 14.2 was used for statistical analysis (Stata Corp., College Station, TX, USA).

Results There were 187 patients (123 women [65.8%], age range ¼ 15–60 years). Their duration of illness was between five and seven days. No complications were noted. A total of 39 (20.85%) were positive for Salmonella bacteraemia. No other bacteria species were detected, 27 (69.23%) being positive for S. typhi and 12 (30.77%)

Tropical Doctor 0(0) Table 1. Clinical characteristic of patients.

Variable Sex (n, male/female) Age (years)* Duration of fever (days)* Leukopenia (n, %) Absence Presence Absolute eosinopenia (n, %)y Absence Presence Thrombocytopenia (n, %)y Absence Presence Elevated AST levels (n, %)y No Yes Elevated ALT levels (n, %)y No Yes Elevated CRP levels (n, %)y No Yes Widal test (n, %) Negative Positive

Negative for Salmonella in the blood (n ¼ 148)

Positive for Salmonella in the blood (n ¼ 39)

49/99 30 (16–60) 5 (5–7)

15/24 27 (15–55) 5 (5–7)

107 (72.3) 41 (27.7)

27 (69.2) 12 (30.8)

79 (53.4) 69 (46.6)

7 (17.9) 32 (82.1)

126 (85.1) 22 (14.9)

25 (64.1) 14 (35.9)

133 (89.9) 15 (10.1)

21 (53.8) 18 (46.2)

133 (89.9) 15 (10.1)

28 (71.8) 11 (28.2)

103 (69.6) 45 (30.4)

11 (28.2) 28 (71.8)

61 (41.2) 87 (58.8)

15 (46.9) 17 (53.1)

Data presented as n (%) of patients in each group, unless otherwise specified. *Data presented as median (range). yP < 0.05 by Chi-square test AST, aspartate aminotransferase; ALT, alanine aminotransferase; CRP, C-reactive protein.

Table 2. Multiple logistic regression model for prediction of Salmonella in the blood. Variable

Odds ratio

95% CI

P

Absolute eosinopenia Elevated AST levels Elevated of CRP levels

4.44 4.84 3.21

1.71–11.50 1.78–11.25 1.35–7.65

0.002 0.001 0.008

AST, aspartate aminotransferase; CRP, C-reactive protein; CI, confidence interval.

for S. paratyphi. Clinical characteristics are shown in Table 1. Multivariate analyses revealed a significant difference in proportion of patients with thrombocytopenia (P ¼ 0.003), absolute eosinopenia (P < 0.001), elevated

Suwarto et al.

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Figure 1. Area under receiver ROC curves of the model prediction for Salmonella in the blood.

aspartate aminotransferase levels (P < 0.001), elevated alanine transaminase levels (P ¼ 0.004), and elevated CRP > 40 mg/L (P < 0.001) between those who were positive and those who were negative for Salmonella by blood culture (Table 1). These five variables noted were then included in multivariate analysis. Furthermore, bivariate analysis indicated a lack of significant difference in leukopenia between the two groups. Predictors of positive blood culture for Salmonella were: absolute eosinopenia; elevated AST levels; and elevated CRP levels (Table 2). The Hosmer–Lemeshow goodness-of-fit test showed that the model for prediction of Salmonella in the blood was well-calibrated (P ¼ 0.95) and the ROC of the model was 80.67% (95% confidence interval [CI] ¼ 72.7–88.6) (Figure 1).

indeed several possible mechanisms of hepatic injury may contribute to typhoid fever pathology.19 CRP is an acute inflammatory marker and is often significantly raised with positive blood cultures.11 Leukopenia was not a helpful marker: this may be because we examined our patients early. Furthermore, no significant difference in positivity of Widal testing was found, probably owing to the endemicity of typhoid.7 Declaration of conflicting interests The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding The author(s) received no financial support for the research, authorship, and/or publication of this article.

Discussion Our study suggests that the combination of clinical findings with laboratory predictors is useful for early diagnosis and quick initiation of appropriate treatment in typhoid fever patients. Absolute eosinopenia has previously been shown as an excellent marker.16 Other investigators have reported that normal absolute eosinophil counts may be used to rule out the possibility of typhoid fever.17 The mechanism of this eosinopenia in enteric fever is not fully understood, but it may be caused by extravasation of eosinophils towards the site of infection due to complement C5a and fibrin activation.18 Elevated transaminase levels have also previously been reported as a most common finding,3 and

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