Laboratory-based surveillance for vancomycin-resistant enterococci: utility of screening stool specimens submitted for Clostridium difficile toxin assay.

OBJECTIVE: To study vancomycin-resistant enterococci (VRE) gastrointestinal colonization prevalence in high-risk hospitalized patients and to assess the cost and utility of this laboratory-based surveillance. SETTING: Large university teaching hospital. DESIGN: Quarterly prevalence culture survey of 50 stool specimens submitted for Clostridium difficile toxin A assay from October 1996 through June 1999 (n=526). Screening culture survey of all C difficile-positive stool specimens from July 1998 through June 1999 (n=140). PATIENTS: Specimens for analysis were collected from patients who were admitted to the hospital and who had C difficile toxin A testing ordered. Patient samples were excluded from analysis if they were obtained from patients not hospitalized at UCLA Medical Center, if the C difficile toxin assay result was indeterminate, or if the patient was known to have previous VRE colonization or infection. RESULTS: During quarterly surveillance, VRE was detected in 19.8%, C difficile toxin A in 9.5%, and both VRE and C difficile toxin A in 3.2% of stool specimens submitted for C difficile toxin assay. Patients whose stool specimens were positive for C difficile toxin A were significantly more likely than those whose specimens were negative to have VRE detected (odds ratio, 2.3; 95% confidence interval, 1.2-4.5). Based on these findings, in July 1998, we began routine screening of all C difficile-positive stool specimens for VRE. From July 1998 through June 1999, 58 (41.4%) of 140 patients with C difficile-positive specimens had VRE newly detected in the stool. The combined cost of the two laboratory-based surveillance strategies was approximately $62 per VRE-positive patient identified and $5,800 per year. CONCLUSION: Quarterly surveillance of stool submitted for C difficile assay combined with screening all C difficile-positive stools is a cost-effective and efficient strategy for detecting VRE stool colonization among high-risk hospitalized patients. Such a laboratory-based surveillance should be included as part of a comprehensive program to limit nosocomial VRE transmission.