Bacterial gastroenteritis in the world of culture-independent diagnostic testing: a study to evaluate the kinetics of bacterial shedding by culture and CIDT

Reliable microbiological diagnosis is important for patient and public health management of bacterial gastroenteritis. Clinical laboratories are adopting culture-independent diagnostic tests (CIDT) widely. We examined the kinetics of bacterial shedding by CIDT and culture following an episode of acute gastroenteritis with one of three prevalent pathogens. The primary outcome was the proportion of samples that tested CIDT-positive or culture-positive at defined time intervals after clinical diagnosis. This longitudinal observational study was conducted in Calgary Health Zone (Alberta, Canada) between 2019 and 2022. Eligible adult patients (≥18 years) were consented and enrolled after a routine public health investigation. Stool samples were submitted at weeks 2, 3, 4, 5, and 6 post-diagnosis. Stools were tested using the commercial nucleic acid-based BD MAX Enteric Bacterial Panel (CIDT method) and routine culture methods. Thirty-seven of 83 enrolled individuals (45%) submitted at least one additional stool. Diagnostic specimens were positive for <i>Campylobacter</i> (<i>n</i> = 19), <i>Salmonella</i> (<i>n</i> = 8), and Shiga toxin-producing <i>Escherichia coli</i> (STEC, <i>n</i> = 10). Median duration of CIDT positivity was 42, 29, and 22 days for <i>Campylobacter, Salmonella,</i> and STEC, respectively. Median duration of culture positivity was 29, 29, and 19.5 days, respectively. Differences between CIDT and culture positivity over time were not statistically significant for <i>Campylobacter</i> (<i>P</i> = 0.23), <i>Salmonella</i> (<i>P</i> = 0.89), and STEC (<i>P</i> = 0.20). A negative CIDT result was 100% predictive of a culture-negative result. Comparing CIDT and culture, no differences in shedding were found between methods in this pilot study. Further larger studies would help better understand the kinetics of CIDT positivity and clinical implications.IMPORTANCEThis study contributes to the limited literature comparing the shedding of common bacterial enteropathogens by culture-independent diagnostic testing (CIDT) methods in comparison to conventional culture. Many clinical microbiology laboratories have implemented CIDT methods for screening stool specimens due to the slower turnaround times and variable sensitivity of culture. Public health agencies often require a negative culture for return-to-work clearance in special situations or sensitive occupations, including food handlers. In our study, we demonstrated that there were no significant differences in the duration of shedding between test methods for three common bacterial pathogens, <i>Campylobacter</i>, <i>Salmonella,</i> and Shiga toxin-producing <i>Escherichia coli</i>. Furthermore, a negative CIDT result was 100% predictive of a negative culture result. This study contributes to the growing body of literature documenting the clinical and public health utility of CIDT in bacterial gastroenteritis.