Epidemiology of Infant Group B Streptococcus Infection in New Zealand: A 10-Year Retrospective Study.

Background: Early-onset Group B Streptococcus (EOGBS) infection is a leading cause of early-onset neonatal sepsis with significant morbidity and mortality. EOGBS is preventable with the administration of intrapartum antibiotic prophylaxis (IAP), recommended in New Zealand (NZ) for laboring women with clinical risk factors for infant infection. Given that there are alternative approaches to IAP eligibility, understanding the current epidemiology of infant Group B Streptococcus (GBS) infection in NZ is essential for optimizing prevention.

Methods: A retrospective study (2012-2021) was conducted on all infants under 180 days old with invasive GBS infection in NZ. Clinical information from the National Collections dataset was matched to laboratory samples (GBS culture/polymerase chain reaction positive on a sterile site). Infection timing was classified as early-onset (≤2 days of life), late-onset (3-89 days) or ultra-late-onset (90-179 days). GBS incidence rates were calculated using Poisson regression.

Results: There were 406 laboratory-confirmed and 224 clinically suspected GBS cases. Although EOGBS incidence was higher than previously described, there was no significant change in incidence over the study period (P = 0.4). EOGBS incidence for Pacific infants was twice that of European infants, with higher rates also found for Māori infants. While no GBS isolates were resistant to penicillin or vancomycin, a third of recent EOGBS isolates were resistant to erythromycin and/or clindamycin. The case-fatality rate was low (2.5%).

Conclusions: The NZ EOGBS prevention program is less effective than previously believed, with unexplained ethnic disparities in infection rates. Identifying gaps in prevention and considering alternative strategies is crucial to reducing infant GBS infection incidence.