Characterization of clostridium difficile infection and analysis of recovered isolates in a community hospital population in Baltimore, Maryland

Background: The emergence of an epidemic strain of Clostridium difficile has been associated with increasing use of fluoroquinolones in clinical medicine, and infection with this strain results in more severe illness, prolonged hospitalization, and increased mortality. Objectives: (1) To characterize C. difficile infection (CDI) among hospitalized patients and (2) to determine in vitro activities of antibiotics against C. difficile isolates among our patient population. Methods: Adult patients were admitted to a community teaching hospital and tested with a C. difficile enzyme immunoassay at admission or upon development of symptoms suggestive of CDI during the period of July 2007 through June 2008. Samples positive for C. difficile toxins A and B were sent to the microbiology laboratory at Johns Hopkins Hospital for toxigenic anaerobic culture, in vitro susceptibility testing, and strain typing by pulsed-field gel electrophoresis. Results: Of 41 patients with a stool sample positive for C. difficile toxins A and B by toxigenic culture, 23 patients (56%) were infected with the epidemic strain of C. difficile (North American pulsed-field type 1 [NAP1]). A significant difference was observed in resistance to levofloxacin in NAP1 strain of C. difficile compared with non-NAP1 isolates (100% vs 72%, P = 0.008). All isolates were susceptible to vancomycin, but NAP1 isolates had higher minimum inhibitory concentrations (MICs; P = 0.02). Metronidazole MICs were also higher in the NAP1 group, but the difference between the 2 groups was only of questionable significance (P = 0.07). Conclusions: The epidemic strain of C. difficile (NAP1) constituted a significant proportion of the infections among our patients with CDI. No resistance was observed against either metronidazole or vancomycin in vitro. All samples positive for the NAP1 strain were resistant to levofloxacin.