Prevalence of group B streptococcus colonization and potential for transmission by casual contact in healthy young men and women.

Group B Streptococcus (GBS) causes disease in newborns, pregnant women, and adults with underlying medical conditions, but it is also a commensal organism that commonly colonizes the bowel. In this study, the prevalence of colonization was high among 241 women (34%) and 211 men (20%) living in a college dormitory; sexually experienced subjects had twice the colonization rates of sexually inexperienced participants. Other predictors of colonization varied by colonization site. Only 10 of the 142 roommate pairs had roommates who were both colonized with GBS, and 20% of these pairs shared identical strains, which is the same rate predicted by the population distribution. By contrast, a previous report found that 86% of co-colonized sex partners shared identical strains. GBS is likely transmitted by intimate contact, but transmission modes may vary by colonization site. Large prospective studies are needed to better understand colonization site-specific factors for GBS and to clarify potential transmission modes.