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Approximately 18% of pregnant women are colonized with Group B streptococcus (GBS), which are β-hemolytic, gram-positive bacteria. GBS conversion from the asymptomatic commensal in the vagina to an invasive pathogen predisposes the pregnant women to ascending intrauterine infection that tiggers preterm birth and initiate fetal and neonatal infections. Here, we review the prevalence of colonizing GBS serotypes and sequence types (STs) in different geographical regions. Maternal components including demographical and obstetric factors that increase the risk for GBS colonization during pregnancy are also further elucidated. The prevalence of colonizing GBS serotypes and sequence types (STs) are elucidated in this review in addition to the maternal components including demographical and obstetric factors that increase the risk for GBS colonization during pregnancy. Investigating the epidemiology is crucial for the development of new therapeutic and preventive measures to reduce the burden of invasive GBS disease worldwide including risk-factor based screening protocols.

Vaginal colonization with Group B streptococcus (GBS) or Streptococcus agalactiae can potentially cause ascending intrauterine infection among pregnant women, and hence it is known as one of the risk factors for preterm delivery. Ascending intrauterine infection may also cause the transmission of GBS to the fetus in utero and the newborn during delivery, leading to the development of early onset of neonatal infection. GBS are β-hemolytic, gram-positive bacteria that are opportunistic commensal of the gastrointestinal and urogenital tract of approximately 18% of pregnant women globally. Intrapartum antibiotic prophylaxis (IAP) only reduces the rate of early onset neonatal infection, but not the late onset neonatal infection. Thus, the development of GBS vaccine is thought to be important to decrease the rate of preterm delivery and neonatal infections particularly in low-and-middle income countries where IAP program is not feasible. Vaccination can also be cost-effective for the healthcare system when executed together with IAP program. The aim of the current review is to summarize the mechanisms on how the GBS virulence factors interact with host immune components in the gestational tissues, leading to cervicovaginal colonization and ascending intrauterine infection. The elucidation of these mechanisms is essential for expediting the development of vaccines and novel therapeutic measures targeting these GBS virulence factors that will hamper the vaginal colonization, ascending intrauterine infection and conceptus tissue invasion by GBS. These strategies are crucial to potentially reduce the rate of preterm delivery and subsequent serious complications in the newborn.