Every Country, Every Woman, Every Child; Group B Streptococcal Disease Worldwide Prematurity modifies the risk of long-term neurodevelopmental impairments after invasive Group B Streptococcus infections during infancy in Denmark and the Netherlands.

Background Preterm birth and neonatal infections are both associated with mortality and long-term neurodevelopmental impairments (NDI). We examined whether the effect of invasive group B streptococcus disease (iGBS) on mortality and long-term NDI differs for preterm and term infants, and whether co-occurrence of iGBS and prematurity leads to worse outcome. Methods Two nationwide cohort studies of children with a history of iGBS were conducted using Danish and Dutch medical and administrative databases. Comparison cohorts of children without iGBS were matched on birth year/month, sex and gestational age. Effects of iGBS on all-cause mortality and NDI were analyzed using Cox proportional hazards and logistic regression, respectively. Potential effect modification by prematurity was evaluated on additive and multiplicative scales. Results We identified 487 preterm and 1,642 term children with a history of iGBS and 21,172 matched comparators. Dutch preterm children exposed to iGBS had the highest mortality rate by 3 months of age (671/1000 person-years [95% confidence interval 412-929/1000 person-years]). ~30% of this mortality rate could be due to the common effect of iGBS and prematurity. Preterm children with iGBS had the highest NDI risk (8.8% in Denmark; 9.0% in the Netherlands). 36% of this NDI risk in Denmark and 60% of this risk in The Netherlands might be due to the combined effect of iGBS and prematurity. Conclusion Prematurity is associated with iGBS development, and our study shows that it also negatively impacts outcomes of children who survive iGBS. Preterm babies would benefit from additional approaches to prevent GBS colonization, as this decreases the risk of both preterm birth and iGBS.