A leading cause of sepsis in neonates, Group B Streptococcus (GBS) is a significant perinatal pathogen. Australian women are screened by culture for this organism in an effort to eradicate colonisation prior to delivery. GBS are separated into ten different capsular polysaccharide serotypes and previous studies have suggested associations between specific serotypes and disease. For example, serotypes Ia, Ib and III are commonly associated with neonatal disease. At present, however, minimal data exists on serotype distribution within Western Australian (WA) women, information that may play an important role in future prophylactic treatment regimes.
Vaginal specimens (n=512) collected from 191 WA women at three gestational ages (18-26, 28 and 36 weeks) during pregnancy were tested retrospectively for GBS. A multiplex real-time PCR assay was developed that universally detected GBS, while concurrently screening for the presence of serotypes Ia, Ib and III. All remaining serotypes were detected using endpoint multiplex PCR as per Imperi et al.1.
21.9% of samples were GBS positive. Serotypes V (22.5%) and III (21.3%) dominated the distribution followed by II (18.7%), Ia (16.2%), VI and IX (both 6.3%), IV (5%), VII (2.5%) and Ib (1.2%). No cps VIII serotypes were detected. 131 women collected samples at every time point, and of these 110 (83.9%) remained consistently positive or negative. Compared to other studies on GBS serotype distribution in eastern Australian states and New Zealand, our WA data showed lower rates of serotype Ib (7-17 times lower), in addition to greater rates of serotypes II (2-6 times greater) and VI (2-12 times greater).
This study provides new insights into circulating GBS serotypes in WA pregnant women. Our data show distinct differences to that seen in other Australian states, information that is potentially vital to successful vaccine development. The observed frequency of consistent colonisation during pregnancy may also support earlier gestation testing for those at risk of delivering preterm, a neonatal population at increased risk of GBS disease.