Differences in Clinical Characteristics and Outcomes of Patients with Community-Onset Clostridium difficile Infection who Tested Positive by EIA Compared with NAAT through a Two-Step Algorithm

BACKGROUND: The low sensitivity of toxin enzyme immunoassay (EIA) for the diagnosis of Clostridium difficile infection (CDI) motivated many laboratories to add nucleic acid amplification tests (NAAT) to their testing protocol. However, NAAT do not distinguish between colonization and infection, and indiscriminant testing could lead to over treatment of CDI. METHODS: Active, population-based CDI surveillance has been conducted through the Emerging Infections Program in Bernalillo County, NM since 2011, with test type collected at the individual level since 2014. Community-onset (CO) CDI cases with a first positive test diagnosed by a two-step algorithm (concurrent EIA/GDH, with discordant results reflexed to NAAT) in 2014–2015 were included. We analyzed clinical characteristics and outcomes of patients EIA positive compared with NAAT positive. Demographics, risk factors, treatment, and outcomes were assessed through medical record review. RESULTS: Among 1,063 cases, 559 (52.6%) were EIA positive only and 504 (47.4%) were NAAT positive only. Of those with stool collected as a hospital inpatient, 57% were NAAT positive (P < 0.001); this increased from 43.4% if tested the day of admission to 61.4% when tested on day three. Conversely, 38.6% of patients with stool collected in an emergency department were NAAT positive (P = 0.004). Fewer cases with complicated outcomes were NAAT positive (40.7%, P = 0.023). Among those with no documentation of recent antibiotic use, 64.3% were NAAT positive (P < 0.001), and 67.8% of cases with no CDI treatment were NAAT positive (P = 0.005). Only 28.3% percent of cases with recurrent CDI were initially NAAT positive (P < 0.001). CONCLUSION: EIA negative and NAAT positive CO-CDI cases tended to have a milder clinical presentation than those that were EIA positive. This suggests that some patients positive only by NAAT may have mild CDI or be colonized, rather than infected, with C. difficile. These individuals were less likely to have complicated outcomes, have recent documented antibiotic use, be treated for CDI, or have a recurrent CDI episode than those positive by EIA. Longer hospital stay correlated with increased proportion of testing NAAT positive. Providers may benefit from considering testing protocol and clinical correlation when assessing patients with positive C. difficile test results. DISCLOSURES: All authors: No reported disclosures.