Background/ hypothesis
Estimates of Group B Streptococcus (GBS) disease burden, antimicrobial susceptibility, and serotypes in pregnant women are limited for many resource-limited countries including Kenya. We evaluated the prevalence, antimicrobial susceptibility patterns, serotypes, and risk factors associated with rectovaginal GBS colonization among pregnant women receiving antenatal care at Kenyatta National Hospital (KNH) between August and November 2017.

Methods
Consenting pregnant women between 12 and 40 weeks of gestation were enrolled. An anorectal swab and a lower vaginal swab were collected and cultured on Granada agar for GBS isolation. Positive colonies were tested for antimicrobial susceptibility to penicillin G, ampicillin, vancomycin, and clindamycin. Serotyping was performed by latex agglutination. Logistic regression was used to identify factors associated with GBS colonization.

Results
A total of 292 women were enrolled. The median age was 30 years (Interquartile range {IQR} 26–35) with a median gestational age of 35 weeks (IQR 30-37). Overall GBS was identified in 20.5% of participants. Antimicrobial resistance was at 72.4% against penicillin G, ampicillin (55.2%), clindamycin (30.4%), and vancomycin (24.1%). All ten GBS serotypes were isolated with 69.8% of GBS-positive participants being colonized by more than one serotype. None of the risk factors was associated with GBS colonization.

Conclusion
The prevalence of GBS colonization was high among antenatal women at KNH with a high proportion of GBS isolates being resistant to commonly prescribed intrapartum antibiotics. Hence, other measures like GBS vaccination are potentially useful approaches to GBS prevention and control in this population. Screening of pregnant mothers for GBS colonization should be introduced and antimicrobial susceptibility tests performed on GBS-positive samples to guide antibiotic prophylaxis