Background: GBS is the leading cause of morbidity and mortality from neonatal sepsis. Vaginal GBS colonisation during labour can cause GBS transmission to neonates in 36% of women, and this can progress to early-onset GBS disease (EOGBS, <7 days) in 1-3% of colonised neonates. We conducted a systematic review investigating whether bacterial load and bacterial molecular markers are associated with GBS vertical transmission, neonatal GBS colonisation, and EOGBS.
Methods: We searched Medline, Embase, Cochrane, and Science Citation Index from inception to 10th October 2016 for observational studies in English. We also hand-searched reference lists of publications and experts cross-checked included studies. Two reviewers independently conducted study selection, data extraction, and quality assessment. Random-effects meta-analyses were conducted where possible.
Results: 19 studies were included from 1107 records. In addition to bacterial load, molecular markers investigated were c-protein antigens, serotypes, and sequence types. Most evidence was published before 2000 and at risk of bias. Meta-analyses showed that neonates colonised by serotype III had a higher risk of developing EOGBS than neonates colonised by serotype Ia (pooled risk ratio [RR] = 1.51, 95% confidence interval [CI] 1.12-2.03) and serotype II (RR = 1.95, 95% CI 1.10-3.45). In twelve studies, neonatal colonisation was approximately 2-3 times higher in heavily colonised mothers, and EOGBS was up to 15 times higher in heavily colonised neonates, compared with light colonisation.
Conclusions: Higher quality studies are needed to assess the predictive value of pathogen subtype and heavy bacterial load; they might be suitable for better-targeted prevention.