Determining Effective Cycle Thresholds for Evaluating Colonization Versus True Infection of Clostridium Difficile Using Xpert Assay
by Drew Siskin
Abstract – Clostridioides difficile is an anaerobic, spore-producing bacterium and is the most common cause of infectious diarrhea in healthcare settings (Lee, 2019). All strains of C. difficile carry the toxin gene; however, only some actually produce toxins, making detection via PCR challenging to differentiate between asymptomatic colonization and symptomatic disease. Therefore, the objective of this study was to explore a current PCR technique, Xpert C. difficile assay, to determine a more precise protocol for doctors to predict true Clostridioides difficile infection (CDI) in a clinical setting. Using previously collected data from 45 PCR- positive CDI patients over spring, 2019 from a New York metropolitan hospital, PCR products of C. difficile toxins A and B were analyzed and compared to their respective patient’s symptoms, which were assessed for severity. Overall, these severity scores showed statistically significant differences, as demonstrated by their associated amplification of the toxin genes, for each of the three conditions (unlikely, mild, and severe infection). Interestingly, a significant relationship was also found between the level of one specific indicator, binary toxin, and severity of infection, corroborating the work of previous research that associated the NAP1/ribotype 027 strain of C. difficile specifically with binary toxin. Overall, our results point to quantifiable statistically significant distinctions via a methodology that uses measured PCR cycle thresholds to distinguish between colonization and true infection. Ultimately, timely and accurate diagnoses of true CDI may lead to more efficient treatments as well as the potential mitigation of antibiotic resistance to Clostridioides difficile.