Bacterial load and molecular markers associated with early-onset Group B Streptococcus

Background: The natural history of neonatal group B Streptococcus (GBS) is poorly understood. Little is known about the bacterial factors influencing the transmission of GBS from mother to neonate, or the development of invasive early-onset GBS disease (EOGBS) in colonized neonates. We reviewed whether bacterial load and molecular markers are associated with GBS vertical transmission and progression to EOGBS. Methods: We searched Medline, Embase, Cochrane and Web of Science from inception to 10th October 2016 for observational studies in English. We also hand-searched reference lists of relevant publications and experts cross-checked included studies. Two reviewers independently screened studies, extracted data and appraised the quality of included studies using the QUIPS tool. We conducted random-effects meta-analyses where possible and narratively synthesized the evidence in text and tables. Results: Seventeen studies were included from 1,107 records retrieved from electronic databases and publication references. Meta-analyses of three studies showed that neonates colonized by serotype III had a higher risk of developing EOGBS than serotype Ia (pooled risk ratio [RR] = 1.51, 95% confidence interval [CI] 1.12 to 2.03) and serotype II (RR = 1.95, 95% CI 1.10 to 3.45). Eleven studies showed that in heavily colonized mothers 2 to 3 times more neonates were colonized, and in heavily colonized neonates up to 15 times more neonates had EOGBS, compared to light colonization. Most evidence was pre-2000 and at risk of bias. Conclusion: Acknowledging the difficulty of natural history studies, well-controlled studies are needed to assess the predictive value of pathogen subtype and heavy load; they may be useful for better-targeted prevention.