Multicenter Evaluation of Clinical Diagnostic Methods for Detection and Isolation of Campylobacter spp. from Stool

The use of culture-independent diagnostic tests (CIDTs), such as stool antigen tests, as standalone tests for the detection ofCampylobacter in stool is increasing. We conducted a prospective, multicenter study to evaluate the performance of stool antigen CIDTs compared to culture and PCR forCampylobacter detection. Between July and October 2010, we tested 2,767 stool specimens from patients with gastrointestinal illness with the following methods: four types ofCampylobacter selective media, four commercial stool antigen assays, and a commercial PCR assay. Illnesses from which specimens were positive by one or more culture media or at least one CIDT and PCR were designated “cases.” A total of 95 specimens (3.4%) met the case definition. The stool antigen CIDTs ranged from 79.6% to 87.6% in sensitivity, 95.9 to 99.5% in specificity, and 41.3 to 84.3% in positive predictive value. Culture alone detected 80/89 (89.9% sensitivity)Campylobacter jejuni/Campylobacter coli -positive cases. Of the 209 noncases that were positive by at least one CIDT, only one (0.48%) was positive by all four stool antigen tests, and 73% were positive by just one stool antigen test. The questionable relevance of unconfirmed positive stool antigen CIDT results was supported by the finding that noncases were less likely than cases to have gastrointestinal symptoms. Thus, while the tests were convenient to use, the sensitivity, specificity, and positive predictive value ofCampylobacter stool antigen tests were highly variable. Given the relatively low incidence ofCampylobacter disease and the generally poor diagnostic test characteristics, this study calls into question the use of commercially available stool antigen CIDTs as standalone tests for direct detection ofCampylobacter in stool.