104 - Evaluation of a 2-Step Testing Algorithm for Clostridioides difficile Infection

Background: A 2-step testing strategy for diagnosis of Clostridioides difficile infection (CDI) is recommended to limit over-diagnosis when clinical criteria requirements for stool sample submission cannot be enforced. Real-world evaluations of this strategy are limited.

Methods: The Antimicrobial Stewardship Program at Brooke Army Medical Center, San Antonio, TX, implemented a 2-step CDI algorithm: polymerase chain reaction (PCR) testing followed by toxin enzyme immunoassay (EIA). The goal was to improve diagnosis of CDI and reduce unnecessary antibiotic use. Patients with PCR+ tests from August 2018 to September 2019 were included. Charts were reviewed for demographics, laboratory data, treatment, and outcomes. Cases were grouped based on concordant (PCR+/EIA+) or discordant (PCR+/EIA-) results. To determine factors contributing to treatment decisions, an analysis of discordant cases were compared by treatment status. Groups were compared by Chi-squared, Fisher’s exact, or Mann-Whitney U tests.

Results: A total of 216 PCR+ tests from 215 patients were recorded. Of these, 155 (71.8%) were discordant. Demographics, laboratory data, and risk factors for CDI were similar between groups (Table 1; p >0.05 for all). Compared to discordant cases, concordant cases were more frequently hospitalized (59% vs 43.9%; p=0.05), had a higher median daily stool count (5 [4-7] vs 4 [2-6], p=0.03), met criteria for severe CDI (33.3% vs 18.7%; p=0.05), received treatment (95.1% vs 66.5%; p< 0.01) and were readmitted in 30 days with CDI (8.3% vs 1.3%; p=0.02). Among discordant cases, median daily stool count was higher in treated vs untreated cases (4 [3-7] vs 3 [1-5], p=0.02). Otherwise, there was no difference in variables according to treatment status (Table 2; p >0.05 for all). Discordant cases with infectious disease (ID) or gastroenterology (GI) consultation had a high rate of treatment (73.9% and 61.1%, respectively).Table 1. Characteristics and outcomes of patients with concordant and discordant tests.
Table 2. Characteristics and outcomes of treated and untreated patients with discordant tests.


Conclusion: Implementation of 2-step strategy reduced antibiotic treatment by nearly 30%. However, the majority of discordant cases were deemed clinically significant and received treatment by providers, including ID or GI specialists. Further studies are needed to determine the unmeasured factors that guide treatment decisions in discordant cases.