Group B streptococcal colonization and transmission dynamics in pregnant women and their newborns in Nigeria: implications for prevention strategies

Objectives Because few studies have been conducted on group B Streptococcus (GBS) in Nigeria, we sought to estimate GBS colonization and transmission frequencies for 500 women and their newborns and identify risk factors for both outcomes. Methods GBS strains were characterized for antibiotic susceptibilities, capsule (cps) genotype, pilus island profile and multilocus sequence type (ST). Results In all, 171 (34.2%) mothers and 95 (19.0%) of their newborns were colonized with GBS; the vertical transmission rate was 48.5%. One newborn developed early-onset disease, yielding an incidence of 2.0 cases per 1000 live births (95% CI 0.50–7.30). Rectal maternal colonization (OR 26.6; 95% CI 13.69–51.58) and prolonged rupture of membranes (OR 4.2; 95% CI 1.03–17.17) were associated with neonatal colonization, whereas prolonged membrane rupture (OR 3.4; 95% CI 1.04–11.39) and young maternal age (OR 2.0; 95% CI 1.22–3.39) were associated with maternal colonization. Women reporting four or more intrapartum vaginal examinations (OR 6.1; 95% CI 3.41–10.93) and douching (OR 3.7; 95% CI 2.26–6.11) were also more likely to be colonized. Twelve STs were identified among 35 mother–baby pairs with evidence of transmission; strains of cpsV ST-19 (n = 9; 25.7%) and cpsIII ST-182 (n = 7; 20.0%) predominated. Conclusions These data demonstrate high rates of colonization and transmission in a population that does not use antibiotics to prevent neonatal infections, a strategy that should be considered in the future.