A nationwide study of invasive Streptococcus agalactiae in the Faroe Islands from 2009 to 2024

Group B Streptococcus (GBS, Streptococcus agalactiae) is a leading cause of invasive disease in neonates, pregnant women, elderly, and immunocompromised individuals. The epidemiology of invasive GBS disease remains poorly documented in small, isolated populations such as the Faroe Islands. This nationwide study assessed invasive GBS cases from 2009 to 2024 in the Faroe Islands. A total of 42 GBS cases were identified. Serotyping was performed using phenotypic assays, with in silico whole-genome sequencing (WGS) based serotype confirmation available for 15 isolates collected between 2020 and 2024. Multilocus sequence typing (MLST), antimicrobial resistance profiling, and virulence gene were also performed. GBS incidence showed an increasing trend over the 15-year period, with the average annual incidence increasing from 3.69 (2009-2018) to 7.47 (2019-2024) per 100,000 population. Predominant serotypes were II, V, Ib, and Ia. All isolates carried genes coding for Alp-family proteins, which are immunogenic targets that may meaningfully influence the effectiveness of future GBS vaccines. MLST revealed a predominance of clonal complex (CC) 12, followed by CC452, CC1, and CC23. Phenotypic testing showed that all isolates were susceptible to penicillin, while four displayed resistance to erythromycin and clindamycin, with two carrying the erm(A) gene. Virulence genes including pilus islands (PI), cfb, sodA, and srr1 were detected. This study establishes a genomic and epidemiological baseline for invasive GBS in the Faroe Islands, highlighting an increase in incidence, data suggesting the likely efficacy of future GBS vaccine candidates, and preserved penicillin susceptibility. Continued genomic surveillance will be essential for informing public health and vaccine policy in small and remote populations.