Objective: We investigated the use of VRE surveillance rectal swabs as a first step toward an active surveillance testing scheme for C. difficile.
Methods: All VRE swabs collected at UPMC Presbyterian from 7/26/09-11/19/09 were secondarily cultured in CCMB-TAL broth media under anaerobic conditions. Swabs were categorized as visibly feculent or not. Fermenting CCMB-TAL tubes were subcultured to sheep blood agar and C. difficile isolates identified by colony morphology and PRO-disc. DNA was extracted from pure isolates by NucliSENS® easyMag® (bioMérieux) and the presence of the toxin B was confirmed by real time PCR detection of tcdB. Field sensitivity of VRE swabs for detection of C. difficile carriage was defined as the proportion of VRE swabs from patients with C. difficile toxin-positive stool by cell culture cytotoxicity assay ± 3 and ±7 days from the VRE swab collection date. Environmental samples were taken from 6 rooms of 5 inpatients with recovery of toxigenic C. difficile who had no history of C. difficile stool testing or contact isolation for other organisms. VRE swab isolates from these 5 patients and their rooms were genotyped by multilocus variable number tandem repeat analysis (MLVA).
Results: Toxigenic C. difficile (CD) was cultured from 383/4976 (7.7%) VRE swabs processed from 3003 patients (142 or 4.7% of patients positive). Of these, 31 patients (21.8%) were already known to be CD+ by stool testing, while 26 (18.3%) had negative stool test(s) and 85 (59.9%) had no history of stool testing. 132/2046 (6.5%) of patients with no CD stool testing history were CD+ on at least one swab at a median 5 days (range 0-48) prior to discharge (971 un-isolated patient-days over study period). Of 2046 patients with no CD stool testing history, 19 (9.3%), 113 (5.5%), and 107 (5.2%) patients were VRE+/CD+, VRE-/CD+, and VRE+/CD-, respectively. CD was recovered from 5/6 rooms sampled at 15/30 sites. At least one environmental isolate matched the patient’s VRE swab isolate in 3/5 patients by MLVA. 46/74 (62%) and 70/142 (49%) swabs collected +/-3 and 7 three days of a positive CD stool test were positive for CD, respectively. Corresponding field sensitivity for visibly feculent swabs was 16/22 (73 %) and 26/41 (63%). An increased interval between swab collection and planting (median 2.5 days, range 1-17 days) did not correlate with reduced field sensitivity.
Conclusions: : Secondary CCMB-TAL culture of VRE surveillance swabs is capable of detecting a large reservoir of hospitalized inpatients asymptomatically colonized with toxigenic C. difficile. Environmental cultures suggest that asymptomatic carriers are capable of hospital transmission to other patients.