Performance of TechLab C. DIFF QUIK CHEK and TechLab C. DIFFICILE TOX A/B II for the detection of Clostridium difficile in stool samples

C. difficile biomarkers, pathogenicity and detection

BACKGROUND

Clostridioides difficile infection (CDI) is the main etiologic agent of antibiotic-associated diarrhea. CDI contributes to gut inflammation and can lead to disruption of the intestinal epithelial barrier. Recently, the rate of CDI cases has been increased. Thus, early diagnosis of C. difficile is critical for controlling the infection and guiding efficacious therapy.

APPROACH

A search strategy was set up using the terms C. difficile biomarkers and diagnosis. The found references were classified into two general categories; conventional and advanced methods.

RESULTS

The pathogenicity and biomarkers of C. difficile, and the collection manners for CDI-suspected specimens were briefly explained. Then, the conventional CDI diagnostic methods were subtly compared in terms of duration, level of difficulty, sensitivity, advantages, and disadvantages. Thereafter, an extensive review of the various newly proposed techniques available for CDI detection was conducted including nucleic acid isothermal amplification-based methods, biosensors, and gene/single-molecule microarrays. Also, the detection mechanisms, pros and cons of these methods were highlighted and compared with each other. In addition, approximately complete information on FDA-approved platforms for CDI diagnosis was collected.

CONCLUSION

To overcome the deficiencies of conventional methods, the potential of advanced methods for C. difficile diagnosis, their direction, perspective, and challenges ahead were discussed.

Prevalence of Clostridioides difficile in Canine Feces and Its Association with Intestinal Dysbiosis

The role of Clostridioides (C.) difficile as an enteropathogen in dogs is controversial. In humans, intestinal bile acid-dysmetabolism is associated with C. difficile prevalence. The relationship between fecal qPCR-based dysbiosis index (DI) and especially the abundance of bile acid-converting Clostridium hiranonis with the presence of C. difficile in dogs was explored across the following 4 cohorts: 358 fecal samples submitted for routine diagnostic work-up, 33 dogs with chronic enteropathy, 14 dogs with acute diarrhea, and 116 healthy dogs. Dogs that tested positive for C. difficile had significantly higher DI (median, 4.4 (range from 0.4 to 8.6)) and lower C. hiranonis (median, 0.1 (range from 0.0 to 7.5) logDNA/g) than dogs that tested negative for C. difficile (median DI, -1 (range from -7.2 to 8.9); median C. hiranonis abundance, 6.2 (range from 0.1 to 7.5) logDNA/g; p < 0.0001, respectively). In 33 dogs with CE and 14 dogs with acute diarrhea, the treatment response did not differ between C. difficile-positive and -negative dogs. In the group of clinically healthy dogs, 9/116 tested positive for C. difficile, and 6/9 of these had also an abnormal DI. In conclusion, C. difficile is strongly linked to intestinal dysbiosis and lower C. hiranonis levels in dogs, but its presence does not necessitate targeted treatment.

A 2-step algorithm combining glutamate dehydrogenase and nucleic acid amplification tests for the detection of Clostridioides difficile in stool specimens

The optimized diagnosis algorithm of Clostridioides difficile infection (CDI) is worldwide concerns. The purpose of this study was to assess the toxigenic C. difficile test performance and propose an optimal laboratory workflow for the diagnosis of CDI in mild virulent epidemic areas. Diarrhea samples collected from patients were analyzed by glutamate dehydrogenase (GDH), toxin AB (CDAB), and nucleic acid amplification test (NAAT). We assessed the performance of GDH, the GDH-CDAB algorithm, and the GDH-NAAT algorithm using toxigenic culture (TC) as a reference method. In this study, 186 diarrhea samples were collected. The numbers of TC-positive and TC-negative samples were 39 and 147, respectively. The sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and kappa of the GDH assay were 100%, 80.3%, 57.4%, 100%, and 0.63; of the GDH-CDAB algorithm were 48.7%, 97.3%, 82.6%, 87.7%, and 0.54; and of the GDH-NAAT algorithm were 74.4%, 100%, 100%, 93.6%, and 0.82, respectively. The GDH-NAAT algorithm has great concordance with TC in detecting toxigenic C. difficile (kappa = 0.82), while the sensitivity of the GDH-CDAB algorithm was too low to meet the demand of CDI diagnosis clinically. GDH-NAAT algorithm is recommended for the detection of toxigenic C. difficile with high specificity, increased sensitivity, and cost-effective.

Consensus on the prevention, diagnosis, and treatment of Clostridium difficile infection

In recent decades, Clostridium difficile infection (CDI) has become a worldwide health problem. Mexico is no exception, and therefore the Asociación Mexicana de Gastroenterología brought together a multidisciplinary group (gastroenterologists, endoscopists, internists, infectious disease specialists, and microbiologists) to carry out the "Consensus on the prevention, diagnosis, and treatment of Clostridium difficile infection", establishing useful recommendations (in relation to the adult population) for the medical community. Said recommendations are presented herein. Among them, it was recognized that CDI should be suspected in subjects with diarrhea that have a history of antibiotic and/or immunosuppressant use, but that it can also be a community-acquired infection. A 2-step diagnostic algorithm was proposed, in which a highly sensitive test, such as glutamate dehydrogenase (GDH), is first utilized, and if positive, confirmed by the detection of toxins through immunoassay or nucleic acid detection tests. Another recommendation was that CDI based on clinical evaluation be categorized as mild-moderate, severe, and complicated severe, given that such a classification enables better therapeutic decisions to be made. In mild-moderate CDI, oral vancomycin is the medication of choice, and metronidazole is recommended as an alternative treatment. In addition, fecal microbiota transplantation was recognized as an efficacious option in patients with recurrence or in the more severe cases of infection, and surgery should be reserved for patients with severe colitis (toxic megacolon), in whom all medical treatment has failed.

Comprehensive evaluation of chemiluminescent immunoassays for the laboratory diagnosis of Clostridium difficile infection

For the microbiological diagnosis of a Clostridium (C.) difficile infection (CDI), a two-test algorithm consisting of a C. difficile glutamate dehydrogenase (GDH)-immunoassay followed by a toxin-immunoassay in positive cases is widely used. In this study, two chemiluminescent immunoassays (CLIAs), one for GDH and the other for the toxins A and B, have been evaluated systematically using appropriate reference methods. Three-hundred diarrhoeal stool specimens submitted for CDI diagnosis were analysed by the LIAISON CLIAs (DiaSorin). Toxigenic culture (TC) and cell cytotoxicity assay (CCTA) were used as "gold standard" reference methods. In addition, GDH and toxin A and B enzyme immunoassays (EIAs), C. diff Chek-60 and toxin A/B II (TechLab), and the Cepheid Xpert C. difficile polymerase chain reaction (PCR) were performed. C. difficile was grown in 42 (14%), TC was positive in 35 (11.7%) and CCTA in 25 (8.3%) cases. CLIAs were more sensitive but less specific than the respective EIAs. Using culture as reference, the sensitivity of the GDH CLIA was 100%. In comparison to CCTA sensitivity, specificity, positive predictive value and negative predictive value of the two-test algorithm were 88, 99.3, 91.7 and 98.9% by CLIAs and 72, 99.6, 94.7 and 97.5% by EIAs. Discrepant results by CLIAs were more frequent than that by EIAs (9% vs. 6.3%); in those cases, PCR allowed for the accurate detection of toxigenic strains. Due to performance characteristics and testing comfort, CLIAs in combination with PCR represent a favourable option for the rapid laboratory C. difficile diagnostics.

Comparison of enzyme immunoassays and rapid diagnostic tests for clostridium difficile glutamate dehydrogenase and toxin a + B to toxinogenic culture on a highly selective chromogenic medium

To compare Clostridium. (C.) difficile toxin A/B and glutamate dehydrogenase (GDH) enzyme immunoassays or rapid diagnostic tests to toxinogenic culture on recently described highly selective agar plates. Five hundred consecutive samples sent in for C. difficile diagnostics were tested by toxin A/B enzyme immunoassay (EIA) and rapid diagnostic test (RDT), GDH EIA and RDT, and culture on chromID C. difficile plates for 48 hrs, with toxin testing from culture if the toxin EIA from feces was negative. Samples with discordant results from EIA and RDT were submitted to C. difficile-specific 16S rRNA gene and tcdB PCR. Ninety-two, 88, 31, and 37 samples were positive by GDH EIA, GDH RDT, toxin A/B EIA, and toxin A/B RDT respectively. Seventy-four samples were positive by culture, 54 culture-positive samples were subjected to repeat toxin testing, with an additional 29 samples positive. Thus, there were 60 C. difficile toxin A/B positive samples in total (12 %). Single-step screening with GDH EIA, GDH RDT, toxin A/B EIA, and toxin A/B RDT would have missed seven (12 %), 11 (18 %), 29 (48 %) or 27 (45 %) of all positive samples respectively. Single-step screening with GDH or toxin A/B tests from feces misses a significant proportion of patients compared to toxinogenic culture, putting these patients at risk from undiagnosed C. difficile infection. More data are needed to establish the clinical significance of a positive toxinogenic culture result in the absence of detectable toxin A/B in feces.

Clostridium difficile infection diagnosis in a paediatric population: comparison of methodologies

The increasing incidence of Clostridium difficile infection (CDI) in paediatric hospitalised populations, combined with the emergence of hypervirulent strains, community-acquired CDI and the need for prompt treatment and infection control, makes the rapid, accurate diagnosis of CDI crucial. We validated commonly used C. difficile diagnostic tests in a paediatric hospital population. From October 2011 to January 2012, 150 consecutive stools were collected from 75 patients at a tertiary paediatric hospital in Perth, Western Australia. Stools were tested using: C. Diff Quik Chek Complete, Illumigene C. difficile, GeneOhm Cdiff, cycloserine cefoxitin fructose agar (CCFA) culture, and cell culture cytotoxin neutralisation assay (CCNA). The reference standard was growth on CCFA or Cdiff Chromagar and PCR on isolates to detect tcdA, tcdB, cdtA, and cdtB. Isolates were PCR ribotyped. The prevalence of CDI was high (43 % of patients). Quik Chek Complete glutamate dehydrogenase (GDH) demonstrated a low negative predictive value (NPV) (93 %). Both CCNA and Quik Chek Complete toxin A/B had poor sensitivity (33 % and 29 % respectively). Molecular methods both had 89 % sensitivity. Algorithms using GDH + Illumigene or GeneOhm reduced the sensitivity to 85 % and 83 % respectively. Ribotype UK014/20 predominated. GDH NPV and GeneOhm and Illumigene sensitivities were reduced compared with adult studies. Quik Chek Complete and CCNA cannot reliably detect toxigenic CDI. A GDH first algorithm showed reduced sensitivity. In a high prevalence paediatric population, molecular methods alone are recommended over the use of GDH algorithm or culture and CCNA, as they demonstrate the best test performance characteristics.

Diagnosis of Clostridium difficile infection: an ongoing conundrum for clinicians and for clinical laboratories

Clostridium difficile is a formidable nosocomial and community-acquired pathogen, causing clinical presentations ranging from asymptomatic colonization to self-limiting diarrhea to toxic megacolon and fulminant colitis. Since the early 2000s, the incidence of C. difficile disease has increased dramatically, and this is thought to be due to the emergence of new strain types. For many years, the mainstay of C. difficile disease diagnosis was enzyme immunoassays for detection of the C. difficile toxin(s), although it is now generally accepted that these assays lack sensitivity. A number of molecular assays are commercially available for the detection of C. difficile. This review covers the history and biology of C. difficile and provides an in-depth discussion of the laboratory methods used for the diagnosis of C. difficile infection (CDI). In addition, strain typing methods for C. difficile and the evolving epidemiology of colonization and infection with this organism are discussed. Finally, considerations for diagnosing C. difficile disease in special patient populations, such as children, oncology patients, transplant patients, and patients with inflammatory bowel disease, are described. As detection of C. difficile in clinical specimens does not always equate with disease, the diagnosis of C. difficile infection continues to be a challenge for both laboratories and clinicians.

Economic evaluation of laboratory testing strategies for hospital-associated Clostridium difficile infection

Clostridium difficile infection (CDI) is the most common cause of infectious diarrhea in health care settings, and for patients presumed to have CDI, their isolation while awaiting laboratory results is costly. Newer rapid tests for CDI may reduce this burden, but the economic consequences of different testing algorithms remain unexplored. We used decision analysis from the hospital perspective to compare multiple CDI testing algorithms for adult inpatients with suspected CDI, assuming patient management according to laboratory results. CDI testing strategies included combinations of on-demand PCR (odPCR), batch PCR, lateral-flow diagnostics, plate-reader enzyme immunoassay, and direct tissue culture cytotoxicity. In the reference scenario, algorithms incorporating rapid testing were cost-effective relative to nonrapid algorithms. For every 10,000 symptomatic adults, relative to a strategy of treating nobody, lateral-flow glutamate dehydrogenase (GDH)/odPCR generated 831 true-positive results and cost $1,600 per additional true-positive case treated. Stand-alone odPCR was more effective and more expensive, identifying 174 additional true-positive cases at $6,900 per additional case treated. All other testing strategies were dominated by (i.e., more costly and less effective than) stand-alone odPCR or odPCR preceded by lateral-flow screening. A cost-benefit analysis (including estimated costs of missed cases) favored stand-alone odPCR in most settings but favored odPCR preceded by lateral-flow testing if a missed CDI case resulted in less than $5,000 of extended hospital stay costs and <2 transmissions, if lateral-flow GDH diagnostic sensitivity was >93%, or if the symptomatic carrier proportion among the toxigenic culture-positive cases was >80%. These results can aid guideline developers and laboratory directors who are considering rapid testing algorithms for diagnosing CDI.

Lack of effect of strain type on detection of toxigenic Clostridium difficile by glutamate dehydrogenase and polymerase chain reaction

Glutamate dehydrogenase (GDH) is popular as a preliminary test for the detection of Clostridium difficile. Recent work has suggested that GDH sensitivity may vary according to ribotype and may be lower for ribotypes 002, 027, and 106 compared with polymerase chain reaction (PCR). We investigated this effect using a dilution series of 64 isolates tested by GDH and Cepheid GeneXpert PCR. PCR was significantly more sensitive than GDH overall; however, there was no difference in detection according to specific ribotype.

Laboratory diagnosis of Clostridium difficile infection can molecular amplification methods move us out of uncertainty?

The laboratory diagnosis of Clostridium difficile infection (CDI) continues to be challenging. Recent guidelines from professional societies in the United States note that enzyme immunoassays for toxins A and B do not have adequate sensitivity to be used alone for detecting CDI, yet the optimal method for diagnosing this infection remains unclear. Nucleic acid amplification tests (NAATs) that target chromosomal toxin genes (usually the toxin B gene, tcdB) show high sensitivity and specificity, provide rapid results, and are amenable to both batch and on-demand testing, but these tests were not universally recommended for routine use in the recent guidelines. Rather, two-step algorithms that use glutamate dehydrogenase (GDH) assays to screen for C. difficile in stool specimens, followed by either direct cytotoxin testing or culture to identify toxin-producing C. difficile isolates, were recommended in one guideline and either GDH algorithms or NAATs were recommended in another guideline. Unfortunately, neither culture nor direct cytotoxin testing is widely available. In addition, this two-step approach requires 48 to 92 hours to complete, which may delay the initiation of therapy and critical infection control measures. Recent studies also show the sensitivity of several GDH assays to be <90%. This review considers the role of NAATs for diagnosing CDI and explores their potential advantages over two-step algorithms, including shorter time to results, while providing comparable, if not superior, accuracy.

Assessment of Clostridium difficile infections by quantitative detection of tcdB toxin by use of a real-time cell analysis system

We explored the use of a real-time cell analysis (RTCA) system for the assessment of Clostridium difficile toxins in human stool specimens by monitoring the dynamic responses of the HS27 cells to tcdB toxins. The C. difficile toxin caused cytotoxic effects on the cells, which resulted in a dose-dependent and time-dependent decrease in cell impedance. The RTCA assay possessed an analytical sensitivity of 0.2 ng/ml for C. difficile toxin B with no cross-reactions with other enterotoxins, nontoxigenic C. difficile, or other Clostridum species. Clinical validation was performed on 300 consecutively collected stool specimens from patients with suspected C. difficile infection (CDI). Each stool specimen was tested in parallel by a real-time PCR assay (PCR), a dual glutamate dehydrogenase and toxin A/B enzyme immunoassay (EIA), and the RTCA assay. In comparison to a reference standard in a combination of the three assays, the RTCA had a specificity of 99.6% and a sensitivity of 87.5% (28 of 32), which was higher than the EIA result (P = 0.005) but lower than the PCR result (P = 0.057). In addition, the RTCA assay allowed for quantification of toxin protein concentration in a given specimen. Among RTCA-positive specimens collected prior to treatment with metronidazole and/or vancomycin, a significant correlation between toxin protein concentrations and clinical CDI severities was observed (R(2) = 0.732, P = 0.0004). Toxin concentrations after treatment (0.89 ng/ml) were significantly lower than those prior to the treatment (15.68 ng/ml, Wilcoxon P = 0.01). The study demonstrates that the RTCA assay provides a functional tool for the potential assessment of C. difficile infections.

Stool studies: tried, true, and new

Much information can be obtained about a patient's gastrointestinal and overall nutritional status through stool samples. Important infectious processes and neoplastic processes are initially identified through diagnostic tests and screening of stool samples. Although in some arenas they are a source of embarrassment and distaste, the value of correctly obtained samples is unquestionable. Patient collaboration with a critical care nurse is integral to obtaining stool samples.

C. Diff Quik Chek complete enzyme immunoassay provides a reliable first-line method for detection of Clostridium difficile in stool specimens

We evaluated a single membrane device assay for simultaneously detecting both Clostridium difficile glutamate dehydrogenase (GDH) and toxin A/B antigens against a standard that combines two PCR assays and cytotoxigenic culture. Results showing dual GDH and toxin A/B antigen positives and negatives can be reported immediately as true positives and negatives, respectively. Specimens with discrepant results for GDH and toxins A/B, which comprised 13.2% of the specimens, need to be retested.

Evaluation of tcdB real-time PCR in a three-step diagnostic algorithm for detection of toxigenic Clostridium difficile

Clostridium difficile is the most common infectious cause of diarrhea in hospitalized patients. The optimal approach for the detection of toxigenic C. difficile remains controversial because no single test is sensitive, specific, and affordable. We have developed a real-time PCR method (direct stool PCR [DPCR]) to detect the tcdB gene encoding toxin B directly from stool specimens and have combined it with enzyme immunoassays (EIAs) in a three-step protocol. DPCR was performed on 699 specimens that were positive for C. difficile glutamate dehydrogenase (GDH) by Wampole C Diff Quik Chek EIA (GDH-Q) and negative for toxins A and B by Wampole Tox A/B Quik Chek EIA (AB-Q), performed sequentially. The performance of this three-step algorithm was compared with a modified "gold standard" that combined tissue culture cytotoxicity (CYT) and DPCR. A separate investigation was performed to evaluate the sensitivity of the GDH-Q as a screening test, and toxigenic C. difficile was found in 1.9% of 211 GDH-Q-negative specimens. The overall sensitivity, specificity, and positive and negative predictive values, respectively, were as follows for an algorithm combining GDH-Q, AB-Q, and DPCR: 83.8%, 99.7%, 97.1%, and 97.9%. Those for CYT alone were 58.8%, 100%, 100%, and 94.9%, respectively. In comparison, the sensitivity and specificity of DPCR were estimated to be 97.5% and 99.7%, respectively, using the same modified gold standard. Neither CYT nor toxin EIA was sufficiently sensitive to exclude toxigenic C. difficile, and combining EIAs with CYT in a three-step algorithm failed to substantially improve sensitivity. DPCR is a sensitive and specific method for the detection of toxigenic C. difficile that can provide same-day results at a cost-per-positive test comparable to those of other methods. A three-step algorithm in which DPCR is used to analyze GDH EIA-positive, toxin EIA-negative specimens provides a convenient and specific alternative with rapid results for 87.7% of specimens, although this approach is less sensitive than performing DPCR on all specimens.

[Comparison of two enzyme immunoassay for detection of Clostridium difficile toxin A and toxin B]

BACKGROUND

Enzyme immunoassay (EIA) capable of detecting both toxin A and toxin B is strongly recommended for the diagnosis of Clostridium difficile associated disease. Therefore, we evaluated two different EIAs for the detection of C. difficile toxin A/B.

METHODS

For a total of 228 stool specimens we performed bacteriologic cultures for C. difficile and examined for toxin A and toxin B using enzyme linked fluorescent immunoassay (ELFA; VIDAS CDAB, Bio-Merieux sa, France) and ELISA (C.DIFFICILE TOX A/B II, TECHLAB, USA). We also performed PCR assays for toxin A and B genes in 117 C. difficile isolates that grew from the stool cultures and compared the results with those obtained with the two different EIAs.

RESULTS

The concordance rate between ELFA and ELISA was 85.5% (195/228). Using the culture and PCR results as the standard, the sensitivity/specificity of the ELFA and ELISA were 65.0%/72.1% and 71.8%/70.3%, and for positive/negative predictive values were 78.4%/69.6% and 71.8%/70.3%, respectively (P value >0.05). No differences were observed between the results of ELFA and ELISA with toxin A(-) toxin B(+) strains of C. difficile.

CONCLUSIONS

The sensitivity of the ELISA was slightly higher than that of ELFA for toxin A and toxin B, but the specificity and positive predictive value of the ELFA were rather higher than those of the ELISA, although no statistical differences were observed. A bacteriologic culture and PCR assay for toxin genes are recommended in case the both EIAs are negative.

Algorithm combining toxin immunoassay and stool culture for diagnosis of Clostridium difficile infection

Enzyme immunoassays (EIA) to detect glutamate dehydrogenase or toxins A (TcdA) and B (TcdB), a cytotoxicity assay, and bacteriologic culture have disadvantages when applied individually to diagnosis of Clostridium difficile infections. Stool specimens (n = 1,596) were subjected to toxin detection via an enzyme-linked fluorescent immunoassay (ELFA; Vidas CDAB assay) and bacteriologic culture for toxigenic C. difficile in a three-step algorithm with additional toxigenic culture. Isolates (n = 163) from ELFA-negative stool specimens were examined via ELFA for toxin production. We amplified tcdA and tcdB from C. difficile isolates and tcdB from stool specimens that were ELFA positive or equivocal and culture negative, and we compared the results to those obtained with the three-step algorithm. More than 26% of stool specimens (419/1,596) were culture positive, yielding 248 isolates (59.2%) with both toxin genes (tcdA- and tcdB-positive isolates), 88 isolates (21.0%) with either tcdA or tcdB, and 83 (19.8%) that had no toxin genes (tcdA- and tcdB-negative isolates). Among 49 (culture-negative/ELFA-positive or -equivocal) stool specimens, 53.1% (26/49) represented tcdB-positive isolates. Therefore, the total number of PCR-positive cases was 362, and 27.1% (98/362) of these were detected through toxigenic culture. The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were 63.3%, 96.7%, 90.5%, and 92.4% (ELFA alone); 92.8%, 93.3%, 80.2%, and 97.8% (culture); and 70.7%, 91.4%, 95.5%, and 100% (three-step algorithm ELFA and bacterial culture with toxigenic culture), respectively, with culture and PCR for tcdA and tcdB as the standards. Thus, sensitivity and specificity were highest using culture and ELFA, respectively, but we recommend the three-step algorithm comprising EIA to detect both toxins and toxigenic culture for C. difficile as a practical method for achieving better PPV and NPV.

Clostridium difficile infection in solid organ transplant recipients

PURPOSE OF REVIEW

To provide a general understanding of Clostridium difficile infection with a focus on recent publications that evaluate the disease in solid organ transplant recipients.

RECENT FINDINGS

The incidence of C. difficile infection is increasing worldwide. Epidemics due to a hypervirulent C. difficile strain are associated with an escalating severity of disease. New evidence further supports basing initial treatment choice on disease severity.

SUMMARY

C. difficile is a significant pathogen in solid organ transplant recipients. Multiple risk factors are found in this population that may result in more severe disease. A high index of suspicion is necessary for the early diagnosis and treatment of C. difficile infection in transplant recipients. Metronidazole and vancomycin show equivalent efficacy in the treatment for mild-to-moderate disease, but vancomycin has demonstrated superiority in the treatment of severe disease. Surgical intervention is also an important consideration in the treatment of solid organ transplant recipients with severe colitis. Rigorous infection control practices are essential for preventing the spread of C. difficile within the hospital environment.

Diagnosis of Clostridium difficile infection by toxin detection kits: a systematic review

Clostridium difficile can be a fatal hospital-acquired infection and its prevalence has increased. Accurate diagnosis of C difficile is essential for patient management, infection control, and for defining its epidemiology. We did a systematic review of commonly used commercial assays for detection of C difficile toxin (CDT) A and B in stool samples. By comparison of detection of CDT in cell culture with or without selective culture for C difficile, the median sensitivities and specificities (IQR) were as follows: Meridian Premier 0.95 (0.86-0.97) and 0.97 (0.95-0.98), TechLab Tox A/B II 0.83 (0.82-0.85) and 0.99 (0.98-1.00), TechLab Tox A/B Quik Chek 0.84 (0.81-0.87) and 1.00 (0.99-1.00), Remel Xpect 0.82 (0.75-0.89) and 0.96 (0.95-0.98), Meridian Immunocard 0.90 (0.84-0.92) and 0.99 (0.98-1.00), and BioMérieux VIDAS 0.76 and 0.93. If the prevalence of CDT A and B in stool samples is relatively low (<10%), the positive predictive value of these assays is unacceptably low (eg, <50% in some circumstances) and will vary depending on the assay and number of samples tested. This low positive predictive value impinges on clinical management, outbreaks, and makes epidemiological data unreliable. To improve diagnosis, we suggest a two-stage testing strategy for C difficile toxin with an initial highly sensitive rapid screening test to identify positive samples that are then confirmed by a reference method.