Material and Method: Pregnant women, gestational age 35 to 37 weeks, who attended antenatal care clinic at Maharaj Nakorn Chiangmai Hospital between May 2015 and March 2016, were prospectively recruited into the study. Lower vaginal and rectal swab specimens were collected to identify the colonization of GBS using standard laboratory technique.

Results: One hundred pregnant women with median age of 30 years (range 14 to 42) were recruited. The prevalence of GBS colonization was 19% (19 in 100 cases). All of the colonized cases were susceptible to penicillin, whereas 26% (5 cases) and 42% (8 cases) surprisingly resisted to erythromycin and clindamycin, respectively. Most of them (16 cases, 84%) had positive culture for vaginal samples but negative for rectal samples. Nevertheless, no case of neonatal GBS infection was observed in the two groups.

Conclusion: The prevalence of GBS colonization in pregnant women was 19%, which was susceptible to penicillin in every case. Most of the cases had culture-positive in vaginal swab specimen. No evidence of GBS-related morbidities was observed in the present study.

Keywords: Group B streptococcus (GBS), Colonization, Pregnant women