Risk factors for group B streptococcal colonization: Potential for different transmission systems by capsular type

PURPOSE: Group B Streptococcus (GBS) is a common inhabitant of the bowel and vaginal flora, with known transmission routes including sexual contact and vertical transmission from mother to infant. Food-borne transmission is also possible, as GBS is a known fish and bovine pathogen. We conducted a prospective cohort study in order to identify risk factors for acquisition. METHODS: We identified risk factors for GBS acquisition among college women (n = 129) and men (n = 128) followed at 3-week intervals for 3 months. RESULTS: A doubling in sex acts significantly increased incidence of GBS capsular type V by 80% (95% confidence interval [CI]: 1.19, 2.58), and other non-la or -Ib types combined by 40% (95% CI: 1.00, 2.06; incidence of capsular type la (odds ratio [OR] = 1.2; 95% CI: 0.71,1.88; p = 0.57) and Ib (OR = 1.5, 95% CI: 0.75, 2.86; p = 0.27) were elevated, although not significantly. After adjustment for sexual activity and sexual history, gender, and eating venue, fish consumption increased risk of acquiring capsular types la and Ib combined 7.3 fold (95% CI: 2.34, 19.50), but not of acquiring other capsular types. Beef and milk were not associated with GBS incidence. CONCLUSIONS: Different GBS capsular types may have different transmission routes.