Carriage of group B streptococcus in pregnant women from Oxford, UK

Objective: To investigate asymptomatic vagino-rectal carriage of group B streptococcus (GBS) in pregnant women. Methods: Women in the final trimester of pregnancy were recruited. A single vagino-rectal swab was taken, with consent, for culture of GBS. Two microbiological methods for isolation of GBS from vagino-ractal swabs were compared. The distribution of capsular serotypes of the GBS identified was determined. Epidemiological data for a subset (n=167) of the pregnant women participating were examined. Results: 21.3% were colonised vagino-rectally with GBS. Risk factors for neonatal GBS disease (maternal fever, prolonged rupture of membranes, and preterm delivery) were present in 34 of 167 women (20.4%), and the presence of these factors correlated poorly with GBS carriage. Capsular serotypes III (26.4%), IA (25.8%), V (18.9%), and IB (15.7%) were prevalent in the GBS isolates. Selective broth culture of vagino-rectal swabs was superior to selective plate culture, but the combination of both methods was associated with increased detection of GBS (7.5%). An algorithm for the identification of GBS from vagino-rectal swabs was developed. Conclusions: GBS carriage is prevalent in pregnant women in Oxfordshire, UK. The poor correlation between risk factors and GBS carriage requires further investigation in larger groups, given that the identification of these surrogate markers is recommended to guide administration of intrapartum antibiotic prophylaxis by the Royal College of Obstetricians of the UK. A selective broth culture detected more GBS carriers than a selective plate culture.