The International Infections in Pregnancy Study: group B streptococcal colonization in pregnant women

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Abstract
Background: Heavy colonization with group B streptococcus (GBS) has been associated with increased risk of preterm birth and neonatal sepsis; the burden of neonatal GBS disease varies geographically. To determine whether variation in heavy colonization and GBS serotypes could contribute to geographic differences in disease burden, we assessed the prevalence of heavy colonization and the distribution of serotypes in asymptomatic pregnant women in multiple countries. Methods: Cervical, lower vaginal and urine samples were collected from women attending seven prenatal clinics in six countries. Light colonization was defined as GBS isolation from Lim broth only; heavy colonization was isolation from urine or sheep blood agar plates. Isolates were serotyped using capillary precipitation. Results: GBS was present in 11.3% of 1308 participants (range 7.1–21.7%); 5.0% were heavily colonized (0.4–18.8%) and 6.4% were lightly colonized (2.9–8.0%). Serotypes III and V were most common (both 17.2%). Serotypes VII and VIII were found in one study center. Conclusions: The prevalence of heavy colonization and GBS serotypes varied significantly among our study centers. Whether this variation could in part explain geographic differences in neonatal morbidity and mortality is a hypothesis that needs further study.