High Frequency of Rifampin Resistance Identified in an EpidemicClostridium difficileClone from a Large Teaching Hospital

Abstract

Background. Rifampin is used as adjunctive therapy for Clostridium difficile–associated disease, and the drug's derivative, rifaximin, has emerged as an attractive antimicrobial for treatment of C. difficile–associated disease. Rifampin resistance in C. difficile strains has been reported to be uncommon. Methods. We examined the prevalence of rifampin resistance among 470 C. difficile isolates (51.1% during 2001–2002 and 48.9% during 2005) from a large teaching hospital. Rifampin sensitivity was performed using E-test. The epidemic BI/NAP1 C. difficile clone was identified by tcdC genotyping and multilocus variable number of tandem repeats analysis. A 200–base pair fragment of the rpoB gene was sequenced for 102 isolates. Data on rifamycin exposures were obtained for all patients. Results. Rifampin resistance was observed in 173 (36.8%) of 470 recovered isolates and 167 (81.5%) of 205 of epidemic clone isolates (P<.001). Six rpoB genotypes were associated with rifampin resistance. Of 8 patients exposed to rifamycins, 7 had rifampin-resistant C. difficile, compared with 166 of 462 unexposed patients (relative risk, 2.4; 95% confidence interval, 1.8–3.3). Conclusions. Rifampin resistance is common among epidemic clone C. difficile isolates at our institution. Exposure to rifamycins before the development of C. difficile–associated disease was a risk factor for rifampin-resistant C. difficile infection. The use of rifaximin may be limited for treatment of C. difficile–associated disease at our institution.