Group B Streptococcus is the leading cause of neonatal disease. This study was sought to determine colonization rate of GBS among pregnant women, and their newborns, serotypes distribution, and vertical transmission rate. A Hospital based cross-sectional study was conducted at Adama Hospital Medical College from June 2014 to October 2014. A total of 280 pregnant women and their newborns were screened for colonization with GBS. Samples were collected from rectovaginal area of pregnant women before delivery, external body parts of newborns. Group B Streptococcus was serotyped by using serotype-specific antisera. A structured questionnaire was used to collect sociodemographic and clinical data of study participants. Maternal and newborns GBS colonization and vertical transmission rate were 13.2% 95% CI (8.9-17.5), 7.4% 95% CI (4.6-10.6) and 56.8% respectively. Serotype distributions of GBS were: Ia, 9(15.5%), Ib, 14(24.1%), II, 16(27.6%), III, 7(12.1%), V, 9(15.5%), VII, 2(3.5%), and non-typeable (NT), 1(1.7%). This study indicated the existence of a primary risk factor for neonatal disease in Adama area. The most prevalent serotype we found in this study was serotype II followed by Ib, Ia and V. As colonizing GBS serotypes could cause invasive disease among newborns, vaccine formulation which includes serotype II, Ia, V, Ib, and III can prevent the invasive disease caused by GBS in the study area.

Keywords: Group B streptococcus, Vertical transmission, Colonization rate, Serotype, Ethiopia