Risk factors for Group B Streptococcus (GBS) Colonisation and Disease in Gambian Women and their Infants

A longitudinal prospective cohort study conducted by investigators from the Vaccines & Immunity Theme at the MRC Unit The Gambia evaluated the prevalence of colonising and invasive disease serotypes of Group B Streptococcus (GBS) in Gambian women and their infants from delivery to three months of age.The results show that GBS colonisation is dominated by serotype V, and carriage and invasive disease rates are comparable to other international sites.

Group B Streptococcus (GBS) is a leading cause of neonatal infection worldwide and transmission occurs mainly from mother to child during the peripartum period. In the African setting, information on GBS disease prevalence remains sparse. Under-identification and under-reporting of GBS cases and deaths appear likely, especially where it is difficult to access healthcare, but GBS is known as one of the leading causes of early-onset neonatal sepsis and meningitis. Maternal colonisation is the leading risk factor for both early and late onset GBS disease, yet in resource-poor countries, little is known about maternal colonisation rates and the prevalent colonising serotypes in African countries. A previous study from the 1990’s showed that serotype (ST) V may be important as both a colonising and invasive disease serotype as it was in the USA in the 1990s, but no data had been collected in The Gambia since. With a vaccine against GBS now on the horizon, it was important to establish which serotypes lead to the carriage and invasive disease in order to insure that the relevant strains will be covered by the vaccine.

Mothers and Babies1

Mothers and their infants awaiting tests

Conducted in two government health centres offering antenatal care to women in Faji Kunda and Jammeh Foundation for Peace Hospitals,750 mothers were recruited between 15th January 2014 and 31st January 2015. Swabs and breastmilk from mothers/infant pairs were collected and cultured on selective agar and all samples were additionally analysed for GBS DNA via real-time PCR to maximise yield. Positive isolates were serotyped using multiplex PCR and gel-agarose electrophoresis. Blood samples were also collected to analyse qualitative and quantitative anti-GBS antibody.

Results from the study show that 253/750 women (33.7%) were GBS-colonised at delivery. The predominant serotypes were: V (55%), II (16%), III (10%), Ia (8%) and Ib (8%). 186 infants were already colonised (24.8%) at birth, 181 (24.1%) at 6 days and 96 at day 60–89 (14%). Infants born before 34 weeks of gestation and to women with rectovaginal and breastmilk colonisation at delivery had increased odds of GBS colonisation at birth. Season of birth was associated with increased odds of persistent infant GBS colonisation (dry season vs. wet season AOR 2.9; 95% CI 1.6–5.2).

The investigators are currently analysing serum samples to identify potential correlates of protection against colonisation, which will be useful in the evaluation of the future GBS vaccines.This work was supported by a Wellcome Trust Clinical Research Fellowship to Dr Kirsty LeDoare, the Thrasher Research Fund, The Medical Research Council (MRC), UK and the Department for International Development (DFID) under the MRC/DFID Concordat arrangement.

Study lead, Dr Kirsty Le Doare,Consultant of Paediatric Infection & Immunity, Wellcome Trust Fellow,Imperial College London said,“I am very excited to be a part of this important project that will improve not only the lives of Gambian mothers and their babies but will help reduce the burden of neonatal disease globally.”

Professor Beate Kampmann, Theme Leader for Vaccines & Immunity stated,“ This project has allowed us to gather up to date information on GBS in West Africa, given that the last studies were conducted over 20 years ago, the results are really timely as new vaccines against the disease are now on the horizon, and we want to make sure that such vaccines will also provide benefits for our population. I am very grateful to Dr Le Doare and the team for the excellent conduct of this study, which now places us right at the table of the GBS science and future developments”

Acknowledgement

We thank the study participants and field workers at Faji Kunda and Jammeh Foundation for Peace Hospitals and MRC Unit The Gambia staff.

Authors

Le Doare, S. Jarju,S. Darboe, F. Warburton, A. Gorringe, P.T. Heath and B. Kampmann

Read more about the study on PubMed Central website on http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4769314/