Prevalence of colonisation with group B Streptococci in pregnant women of a multi-ethnic population in the Netherlands

Objective: This study was performed to determine the prevalence of GBS and to identify GBS colonisation risk factors in a multicultural population of pregnant women in The Netherlands. We calculated predictive values of cultures in pregnancy for intrapartum GBS carriage. Study design: From a total of 1702 women visiting several antenatal outpatient departments, rectovaginal swabs were collected at 35-37 weeks' gestation. In 761 women swabs were repeated at time of delivery. Carriage of GBS late in third trimester and at time of delivery was analysed in relation to age, parity, ethnicity and socio-economic status. Results: Twenty-one percent was GBS carrier late in pregnancy. Compared to Europeans, African women were at a higher risk (29%, RR 1.4, CI 1.1-1.7) and Asian women were at lower risk (13%, RR 0.6, CI 0.4-0.8) for GBS carriage. No differences in colonisation were found between women with respect to age, parity or socio-economic background. Positive predictive value of GBS carriage at 35-37 weeks' gestation for carriage at time of parturition was 79% and negative predictive value was 93%. Conclusions: It was not possible to identify a group of pregnant women at high risk for GBS colonisation. Predictive values of antenatal genital group B streptococci cultures at 35-37 weeks' gestation for intrapartum GBS carriage are lower than previously reported.