Differential rates of group B streptococcus (GBS) colonisation in pregnant women in a racially diverse area of London, UK: a cross‐sectional study

To describe the epidemiology of maternal group B streptococcus (GBS) colonisation by racial group.Cross-sectional study.Antenatal clinics in London North West University Healthcare NHS Trust.Pregnant women.Group B streptococcus (GBS) colonisation status was recorded during a screening programme for the prevention of invasive early-onset GBS infection. Information regarding age, address, ethnicity, parity, mode of delivery, body mass index (BMI), and diabetes was routinely collected. Data were analysed by multivariable analysis.Association between GBS colonisation and putative risk factors.Overall, 29.1% (1836/6309) of the women were colonized with GBS. Multivariable analysis showed significantly higher colonisation among women of black African origin (39.5%; OR = 1.57) compared with white British women (27.4%), and lowest colonisation in women of South Asian origin (23.3%; OR = 0.8). Higher parity (≥2) was associated with higher colonisation (35.3%), with the odds of colonisation over 40% higher than for nulliparous women. Increasing BMI was associated with an incremental rise in colonisation from 23 to 35%. Colonisation was not associated with age, season or mode of testing.This study identified high maternal GBS colonisation rates in a racially and socially diverse population. The highest rates were seen in women of black African origin and also with higher parity and BMI. Further research is needed to understand the relationship between these factors and rectovaginal colonisation.Study of group B streptococcus colonisation in pregnant women in London shows highest rates in black African women and those with high BMI and parity.