High rate of false-negative results of the rectal swab culture method in detection of gastrointestinal colonization with vancomycin-resistant enterococci

Abstract

The diagnostic accuracy of the rectal swab (RS) culture method in identifying gastrointestinal colonization with vancomycin-resistant enterococci (VRE) is not known. Serial quantitative stool cultures, skin cultures, and RS cultures were performed for patients with VRE infections to assess the false-negative rate of the RS and the prevalence of skin colonization, a prerequisite for cross-transmission, at varying VRE stool densities. A total of 35 stool samples were obtained from 13 patients. The sensitivity of the RS culture was 58%; it ranged from 100%, at VRE densities of 7.5 log10 colony forming units (cfu) per gram of stool, to 0%, at densities of 4.5 log10 cfu per gram of stool. Skin colonization was detected at these low VRE stool densities, but it was more common at higher VRE densities (P< .001). Antibiotic exposure was significantly associated with higher VRE stool densities (P< .001). The high false-negative rate of the RS may be contributing to the continued increase in the prevalence of VRE.