<p><strong>BACKGROUND: </strong>Determine the incidence of GBS disease among extremely preterm infants and assess risk of death or neurodevelopmental impairment (NDI) at 18-26 months' corrected age.</p>

<p><strong>METHODS: </strong>Observational cohort study of infants enrolled in a multicenter registry. GBS disease incidence was assessed in infants born 1998-2016 at 22-28 weeks' gestation surviving &gt;12 hours. The composite outcome, death or NDI, was assessed in infants born 1998-2014 at 22-26 weeks' gestation. Infection was defined as GBS isolation in blood/CSF culture at ≤72 hours (early-onset disease, EOD) and &gt;72 hours (late-onset disease, LOD) after birth. The outcome was compared in infants with GBS disease, infants infected with other pathogens, and uninfected infants using Poisson regression models.</p>

<p><strong>RESULTS: </strong>Incidence of GBS EOD (2.70/1000 births [95% CI: 2.15-3.36]) and LOD (8.47/1000 infants [7.45-9.59]) did not change significantly over time. The adjusted relative risk (aRR, 95% CI) of death/NDI was higher among GBS EOD cases compared to infants with other infections (1.22, [1.02-1.45]) and uninfected infants (1.44, [1.23-1.69]). Death/NDI did not differ between infants with GBS LOD and comparator groups. GBS LOD occurred at a significantly later age than non-GBS late-onset infection. Among infants surviving &gt;30 days, the risk of death was higher with GBS LOD (1.90, [1.36-2.67]), compared to uninfected infants.</p>

<p><strong>CONCLUSIONS: </strong>In a cohort of extremely preterm infants, incidence of GBS disease did not change during the study period. Increased risk of death/NDI with GBS EOD, and of death among some infants with GBS LOD, supports the need for novel preventive strategies for disease reduction.</p>