ELSEVIER BACTERIOLOGY zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Increased Recovery of Group B Streptococcus by the Inclusion of Rectal Culturing and Enrichment Mark W. Platt, James C. McLaughlin, George J. Gilson, Mary F. Wellhoner, and Linda J. Nims zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Defection of intrapartum carriage of group B streptococcus (GBS) and subsequent antibiotic prophylaxis may prevent GBS infections in neonates. Because the gastrointestinal tract is the primary source of this organism, detection of carrier status requires both rectal and vaginal swabs. Vaginal swabs from 652 obstetric outpatients were plated onfo 5% sheep blood agar. A second vaginal and a rectal swab were collected and incubated overnight in an enrichment medium of Todd-Hewitt broth containing antibiotics. By at least one method, 220 (16.9% ) patients were positive for GBS. Only 31.8% of these positive patients were detectedby direct culture of vaginal swabs. The use of vaginal swabs directly plated onto blood agar identified only three carriers not detected by another method. lnoculafion of an enrichment broth with the vaginal INTRODUCTION During the last 2 decades, group B Streptococcus (GBS) has emerged as a major neonatal pathogen (Baker and Edwards, 1990; Platt and Gilson, 1994). From the Departments of Microbiology (M.W.P.) and Pa- thology and Microbiology (J.C.M.), School of Medicine, and Department of Obstetrics and Gynecology, University Hospi- tals (G.J.G., M.F.W.), University of New Mexico Health Sci- ences Center; and Scientific Laboratory Division, New Mexico Department of Health (L.J.N.), Albuquerque, New Mexico, USA. This work was presented in part at the 94th Annual Meet- ing of the American Society for Microbiology, Las Vegas, Ne- vada, May 1994. Address reprint requests to Dr. M.W. Platt, Department of Microbiology, School of Medicine, University of New Mexico Health Sciences Center, Albuquerque, NM 87131, USA. Received 11 October 1994; revised and accepted 11 January 1995. DIAGN MICROBIOL INFECT DIS 1995;21:65-68 0 1995 Elsevier Science Inc. 655 Avenue of the Americas, New York, NY 10010 swab and subsequent subculture detected 70.9% of the fofal. The use of both vaginal and rectal swabs with enrichment de- tected 97.3% of total GBS carriers. A subset of enrichment broths inoculated with vaginal and rectal specimens from 279 patients was tested for GBS by direct latex agglutination Wreptex; Murex Diagnostics, Inc., Norcross, GA, USA). Of the 90 broths that grew GBS on subculture, only 59 (65.6% ) were positive by the direct agglutination method. The use of this method, although reducing processing time by 1 day, gave false-negative results for one-third of the GBS-positive broths. An accurate detection of the GBS carrier state can only be achieved by a combination of vaginal and rectal swabs incu- bated in enrichment broth and subcultured on blood agar. The ease of treatment by antepartum chemoprophy- laxis compared with the high morbidity and mortal- ity of the disease in newborns means that accurate and timely detection of maternal colonization can be used to identify candidates for antepartum chemo- prophylaxis (Platt and Gilson, 1994). Badri et al. (1977) demonstrated conclusively that the rectum is the source of vaginal colonization, with GBS being present almost twice as frequently in rectal as in vaginal cultures. Rapid tests have been deveIoped for GBS detection; these include an enzyme-based immunoassay and a latex agglutination test. When these commercial reagents were tested in hospital situations, they were shown to have a sensitivity too low for clinical use in the detection of carriers (Green et al., 1993; Kontnick and Edberg, 1990). In addition to low sensitivity, according to the manu- 0732-8893/ 951$9.50 SSDI: 0732~8893(95)00022-3