Cycle thresholds and discordant 2-step testing for Clostridioides Difficile: Comparison of clinical characteristics and outcomes among discordant and true positive results

Objective: To determine if Toxin B polymerase chain reaction (PCR) cycle threshold (Ct) can help identify which patients with discordant clostridioides difficile (CD) PCR and enzyme immunoassay testing (EIA) may benefit from treatment. Design: Retrospective case series. Setting: Multi-hospital tertiary Academic system. Patients: All admitted adult patients with positive CD PCR over a 6 month period (n = 214). Patients with positive Stool PCR for other pathogens were excluded. Methods: Chart review of all eligible patients. CD testing results, patient demographics, underlying comorbidities, symptoms prompting testing, risk factors for CD, markers of severe disease, treatment regimens, and clinical outcomes including: 30-day all-cause mortality and re-admission, and 60-day CDI repeat testing and treatment were collected. Results: Significant association between mortality and lower Ct values among discordant patients who were not treated compared to those who were (P = 0.042). The association between Ct values and 30-day readmission was significantly stronger among untreated patients compared to those who were treated (P = .034). A similar trend was observed among non-severe, untreated patients with low Ct values and subsequent CDI treatment within 60 days (CT < 26, 49% vs. CT > 26, 18%, P = .063). Conclusions: Untreated patients with lower cycle thresholds had worse clinical outcomes compared to untreated patients with higher Ct, regardless of disease severity. A lower PCR Ct can support treatment in patients with clinical disease, positive PCR and negative toxin EIA.