Molecular Epidemiology of Group B Streptococcus Colonisation and Neonatal Sepsis Risk in Pregnant Women in South West Nigeria

Group B Streptococcus (GBS) maternal colonisation is the primary risk factor for early-onset neonatal GBS sepsis, yet molecular epidemiology data on GBS serotype distribution and colonisation rates in South West Nigerian pregnant women are absent from the literature. This study determines the prevalence, serotype distribution, and antimicrobial susceptibility of GBS in pregnant women at 35 to 37 weeks gestation in Lagos and Ogun States, South West Nigeria. A cross-sectional study enrolled 300 women from whom recto-vaginal swabs were collected. GBS was isolated on chromogenic GBS agar and confirmed by CAMP test. Serotyping was performed by latex agglutination, and susceptibility was tested against penicillin, ampicillin, clindamycin, and erythromycin. Intrapartum risk factors for neonatal GBS sepsis and neonatal outcomes were documented. GBS colonisation prevalence was 18.7 percent. Serotypes Ia (32 percent), III (28 percent), and V (22 percent) predominated. All isolates were susceptible to penicillin, though clindamycin resistance was 24 percent and erythromycin resistance 31 percent. Neonates born to GBS-positive mothers without intrapartum prophylaxis had a 4.1-fold higher early-onset sepsis rate. The study establishes the first molecular GBS epidemiology dataset for South West Nigeria and demonstrates the necessity for universal late-pregnancy GBS screening and intrapartum penicillin prophylaxis policy development. Keywords: Group B Streptococcus, colonisation, neonatal sepsis, South West Nigeria, intrapartum prophylaxis