ADS 27 - Analysis of Two-step Clostridioides Difficile Testing on Case Reporting, Cycle Threshold Value and Treatment Choice

Background: Various strategies for diagnosing Clostridioides difficile (CD) differ in their sensitivity and specificity, as well as ability to distinguish colonization from infection. Impacts include reducing the number of National Healthcare Safety Network (NHSN)-reportable cases, and potentially affecting provider prescribing practices

Methods: To increase the specificity of CD diagnoses and to better identify the patient population in need for treatment, our institution moved from single-step polymerase chain reaction (PCR) testing to a two-step process whereby PCR-positive sample are subsequently tested for the presence of the CD toxin. Results were entered into the electronic medical record as negative, PCR-positive/toxin-negative (P+/T-) or PCR-positive/toxin-positive (P+/T+). To determine the impact of these results on provider prescribing habits, we counted oral vancomycin doses prescribed to patients with P+/T- versus P+/T+ results. We also compared the PCR cycle threshold (Ct) values of P+/T- versus P+/T+ samples.

Results: As anticipated, the number of hospital-onset cases reportable to NHSN declined; out of 116 PCR-positive samples, only 37 (31.9%) were also toxin-positive. Our data showed that 98% of patients with P+/T+ results were prescribed at least a 10-day course of oral vancomycin, while 43.2% of P+/T- patients also were prescribed at least a 10-day course. In this P+/T- group, an additional 30.9% received a 1-9 day course of oral vancomycin. The mean Ct values were significantly different between the two groups (31.1 versus 24.6, respectively, p < < 0.01).

Conclusions: These studies show that two-step testing resulted in fewer NHSN-reportable cases. However, 74.2% of patients received 1-10 days of vancomycin despite being P+/T-. Possible explanations include concerns about the lower sensitivity of the toxin assay and concern about severe outcomes in immunocompromised patients. Our data also suggest that review of Ct values could help providers re-assess the likelihood of CD disease in P+/T- patients, and allow for consideration of alternate diagnoses.