171 Role of Toxin A/B and GDH Negativity Differentiating Colonization Versus Active Infection in Presence of Positive PCR Results

Abstract

INTRODUCTION: 2018 IDSA guidelines recommend testing for Clostridioides difficile infection (CDI) in patients with 3 loose bowel movements in 24 hours and known risk factors for CDI. Optimal testing strategy is not clear although a two-step algorithm is now recommended: glutamate dehydrogenase [GDH] plus toxin EIA; GDH plus toxin, arbitrated by PCR; or PCR plus toxin. C. diff PCR is a sensitive test and can indicate CDI but also may reflect colonization. Many institutions use PCR testing solely in CDI diagnosis, leading to potential overdiagnosis. The aim of this study was to determine, among patients with positive PCR samples at Meridian hospitals, whether a positive GDH and toxin would correlate better with clinical diagnosis of CDI than positive PCR/neg GDH. METHODS: Chart reviews of patients positive for toxigenic C.Diff by PCR that detects the tcdC gene was performed. Positive PCR samples were also tested for GDH and toxin A/B by enzyme immunoassay (EIS) using C. DIFF QUIK CHEK COMPLETE (QCC; TechLab, Blacksburg, VA, USA) between 12/2018 and 1/2019 at our institution. Clinical and lab data were obtained to help determine accuracy of lab test results. RESULTS: 110 patients were positive for PCR and tested also for GDH/toxin. 73 (66%) were female, mean age was 67 years. Primary outcome: 16% (n = 18) were PCR positive but negative for both GDH and Toxin A/B. Among the 92 who were [GDH+], 45 (49%) were also [toxin A/B+]. Among those who were [GDH+] and [GDH−], at the time of diagnosis there were no statistically significant differences between the following: temperature, leukocytosis, creatinine or albumin at time of diagnosis, prior history of CDI, active malignancy, PPI use, recent laxative use, enteral nutrition or iodinated oral contrast (Tables 1 and 2). The mean number of days until diarrhea resolution was longer among [GDH-] (n = 18, 5.3 days) versus [GDH+] (n = 81, 3.6 days). Most patients were treated with oral Vancomycin. CONCLUSION: This data shows that a positive PCR for CDI was associated up to a 16% false positive rate with negative GDH. GDH status was not associated with significant differences in measured variables. The primary strength is this is the largest cohort reporting this type of analysis. The limitations of the study include incomplete retrospective clinical data obtained from EMR notes regarding morbidities that could explain the differences in time to resolution of diarrhea. Further study with more data is warranted and subset analysis of GDH+ with +/− Toxin EIA should be done.