Optimal screening strategies, colonization rates, and antimicrobial resistance within a newly implemented organized...

Streptococcus agalactiae (group B Streptococcus, GBS) is a major cause of early-onset neonatal infections, with maternal GBS colonization being the primary risk factor. Despite a neonatal GBS incidence exceeding the global average, Slovenia lacked an organized national screening program in pregnant women until 2023. This study presents the first screening results within the newly implemented program.

Between July 2023 and January 2026, 11,248 combined vaginal-rectal swabs from 10,839 women (11,194 pregnancy episodes) were processed at the Institute of Microbiology and Immunology, University of Ljubljana. All samples were tested using enriched culture with Todd-Hewitt broth and chromogenic medium. During the first seven months, reflex molecular testing (Alethia® GBS LAMP-assay after enrichment) was additionally performed in culture-negative samples. Antimicrobial susceptibility testing was conducted on all GBS isolates.

GBS colonization was detected by culture in 1,809/11,194 (16.1%) pregnancy episodes. In 111/1,809 culture-positive results, GBS was only detected after enrichment. During the reflex molecular testing period, additional colonizations were identified solely by molecular testing performed after enrichment, resulting in a relative increase of approximately 10% compared to culture alone. Resistance to clindamycin and erythromycin was found in 19.7% and 19.9% of isolates, respectively; no penicillin or vancomycin resistance was observed.

Optimal antenatal screening requires combined vaginal-rectal swabs and enriched culture with chromogenic media. Adjunctive molecular diagnostics significantly increases GBS detection compared to enriched culture alone. Sustained investment in accurate screening advances both improved perinatal outcomes and antimicrobial stewardship.