Expert Review of Molecular Diagnostics Downloaded from informahealthcare.com by Nyu Medical Center on 06/21/15 For personal use only.
Diagnostic Profile
Portrait Toxigenic Clostridium difficile assay, an isothermal amplification assay detects toxigenic C. difficile in clinical stool specimens Expert Rev. Mol. Diagn. 14(1), 17–26 (2014)
Gerald A Denys Department of Pathology and Laboratory Medicine, Division of Clinical Microbiology, Indiana University School of Medicine, 350 West 11th Street, Room 6027B, Indianapolis, IN, USA Tel.: +1 317 491 6296 [email protected]
The Portrait Toxigenic Clostridium difficile assay is a rapid, qualitative assay for the detection of the tcdB gene of C. difficile in stool specimens from patients suspected of C. difficile infections, and received 510(k) clearance by the US FDA in March 2012. The Portrait Toxigenic C. difficile assay combines novel blocked-primer-mediated helicase-dependent multiplex amplification (bpHDA) technology and chip-based detection in an automated sample-to-result format. The assay requires minimal sample preparation and results are available within 90 min. In a multicenter evaluation, the Portrait Toxigenic C. difficile assay had a sensitivity of 98.2% and specificity of 92.8% compared with toxigenic culture. A comparative study between the Portrait Toxigenic C. difficile assay and three FDA-cleared molecular assays for the detection of toxigenic C. difficile exhibited a high degree of agreement (93.8–97.5%). The Portrait Toxigenic C. difficile assay provides a simple, cost-effective method with broad applicability to panel-based approaches, potentially simplifying workflow. KEYWORDS: Clostridium difficile • C. difficile infections • diagnostic test • helicase-dependent amplification • isothermal tcdB amplification • nucleic acid amplification tests • Portrait Toxigenic C. difficile assay • sensitivity, specificity • toxigenic culture
Clostridium difficile is an anaerobic, Gram-positive, spore-forming, rod-shaped bacterium that can be found in soil and the gastrointestinal tract of animals and humans. It is usually spread by the fecal-oral route, is non-invasive and produces toxins. The spore form of C. difficile remains dormant in the environment and is resistant to antibiotics while the vegetative form can produce toxins. Toxigenic C. difficile strains contain genes on the pathogenicity locus (PaLoc) that encode various toxins including the large clostridial toxins A and B [1]. C. difficile infection (CDI) caused by toxinproducing strains can range from mild diarrhea to severe pseudomembranous colitis, toxic megacolon, sepsis and death [2,3]. Diagnostic testing for CDI should be limited to patients with clinically significant diarrhea since asymptomatic colonization with C. difficile has also been reported [4–6]. The hallmark of symptomatic
www.expert-reviews.com
10.1586/14737159.2014.864239
illness is watery, non-bloody diarrhea with three or more stools within 24 h in patients with risk factors [4,7]. Risk factors for CDI include antibiotic use, advanced age (>65), increased severity of underlying illness, prior hospitalization, use of feeding tubes, gastrointestinal surgery and use of proton-pump inhibitors [2,8]. Since the early 2000s, the incidence and severity of CDI has increased dramatically [9–14]. Hospitalized patients receiving antibiotic therapy are at greater risk for CDI, however, rates of community-acquired CDI have also increased [12,15,16]. In the USA, the economic burden of CDI on the healthcare system is estimated to be US$3.2 billion annually [17,18]. Organizations such as the IDSA/SHEA and European Society of Clinical Microbiology and Infectious Diseases (ESCMID) provide guidelines for the diagnosis and management of patients with CDI and recommendations for the prevention and control
Ó 2014 Informa UK Ltd
ISSN 1473-7159
17
Diagnostic Profile
Denys
Expert Review of Molecular Diagnostics Downloaded from informahealthcare.com by Nyu Medical Center on 06/21/15 For personal use only.
Table 1. Advantages and disadvantages of diagnostic tests for the laboratory diagnosis of Clostridium difficile infection. Test
TAT (h)
Level of difficulty
Sensitivity
Advantages
Disadvantages
Clostridium difficile culture
24–72
Easy
Low
Detects C. difficile Moderate specificity
Time consuming Does not distinguish toxin-producing strains
CCCNA
24–48
Hard
High
Detects toxin A, B High specificity
Time consuming Labor intensive
TC
>96
Moderate to hard
High
Reference method Detects C. difficile toxin-producing strains High specificity
Time consuming Labor intensive
Toxin EIA
Diagnostic Profile
Portrait Toxigenic Clostridium difficile assay, an isothermal amplification assay detects toxigenic C. difficile in clinical stool specimens Expert Rev. Mol. Diagn. 14(1), 17–26 (2014)
Gerald A Denys Department of Pathology and Laboratory Medicine, Division of Clinical Microbiology, Indiana University School of Medicine, 350 West 11th Street, Room 6027B, Indianapolis, IN, USA Tel.: +1 317 491 6296 [email protected]
The Portrait Toxigenic Clostridium difficile assay is a rapid, qualitative assay for the detection of the tcdB gene of C. difficile in stool specimens from patients suspected of C. difficile infections, and received 510(k) clearance by the US FDA in March 2012. The Portrait Toxigenic C. difficile assay combines novel blocked-primer-mediated helicase-dependent multiplex amplification (bpHDA) technology and chip-based detection in an automated sample-to-result format. The assay requires minimal sample preparation and results are available within 90 min. In a multicenter evaluation, the Portrait Toxigenic C. difficile assay had a sensitivity of 98.2% and specificity of 92.8% compared with toxigenic culture. A comparative study between the Portrait Toxigenic C. difficile assay and three FDA-cleared molecular assays for the detection of toxigenic C. difficile exhibited a high degree of agreement (93.8–97.5%). The Portrait Toxigenic C. difficile assay provides a simple, cost-effective method with broad applicability to panel-based approaches, potentially simplifying workflow. KEYWORDS: Clostridium difficile • C. difficile infections • diagnostic test • helicase-dependent amplification • isothermal tcdB amplification • nucleic acid amplification tests • Portrait Toxigenic C. difficile assay • sensitivity, specificity • toxigenic culture
Clostridium difficile is an anaerobic, Gram-positive, spore-forming, rod-shaped bacterium that can be found in soil and the gastrointestinal tract of animals and humans. It is usually spread by the fecal-oral route, is non-invasive and produces toxins. The spore form of C. difficile remains dormant in the environment and is resistant to antibiotics while the vegetative form can produce toxins. Toxigenic C. difficile strains contain genes on the pathogenicity locus (PaLoc) that encode various toxins including the large clostridial toxins A and B [1]. C. difficile infection (CDI) caused by toxinproducing strains can range from mild diarrhea to severe pseudomembranous colitis, toxic megacolon, sepsis and death [2,3]. Diagnostic testing for CDI should be limited to patients with clinically significant diarrhea since asymptomatic colonization with C. difficile has also been reported [4–6]. The hallmark of symptomatic
www.expert-reviews.com
10.1586/14737159.2014.864239
illness is watery, non-bloody diarrhea with three or more stools within 24 h in patients with risk factors [4,7]. Risk factors for CDI include antibiotic use, advanced age (>65), increased severity of underlying illness, prior hospitalization, use of feeding tubes, gastrointestinal surgery and use of proton-pump inhibitors [2,8]. Since the early 2000s, the incidence and severity of CDI has increased dramatically [9–14]. Hospitalized patients receiving antibiotic therapy are at greater risk for CDI, however, rates of community-acquired CDI have also increased [12,15,16]. In the USA, the economic burden of CDI on the healthcare system is estimated to be US$3.2 billion annually [17,18]. Organizations such as the IDSA/SHEA and European Society of Clinical Microbiology and Infectious Diseases (ESCMID) provide guidelines for the diagnosis and management of patients with CDI and recommendations for the prevention and control
Ó 2014 Informa UK Ltd
ISSN 1473-7159
17
Diagnostic Profile
Denys
Expert Review of Molecular Diagnostics Downloaded from informahealthcare.com by Nyu Medical Center on 06/21/15 For personal use only.
Table 1. Advantages and disadvantages of diagnostic tests for the laboratory diagnosis of Clostridium difficile infection. Test
TAT (h)
Level of difficulty
Sensitivity
Advantages
Disadvantages
Clostridium difficile culture
24–72
Easy
Low
Detects C. difficile Moderate specificity
Time consuming Does not distinguish toxin-producing strains
CCCNA
24–48
Hard
High
Detects toxin A, B High specificity
Time consuming Labor intensive
TC
>96
Moderate to hard
High
Reference method Detects C. difficile toxin-producing strains High specificity
Time consuming Labor intensive
Toxin EIA
