From Colonization to Invasive Disease

Background: Group B Streptococcus (GBS), traditionally regarded as a pathogen of neonates and pregnant women, is increasingly recognised as an important cause of invasive and noninvasive disease among nonpregnant adults, especially with advanced age and underlying comorbidities. The study aimed to characterize the clinicomicrobiological profile, comorbidities, antimicrobial susceptibility patterns, and outcomes of GBS infections in a tertiary-care hospital in South India. Methods: This prospective, laboratory-based study was conducted from August 2022 to January 2024. A total of 150 consecutive, nonduplicate GBS isolates from routine clinical specimens, including vaginal swabs, were identified using MALDI-TOF. Antimicrobial susceptibility testing was performed using the VITEK 2 Compact and Kirby-Bauer disk diffusion, and interpreted according to the CLSI M100 2022 and 2023 guidelines. Demographic and clinical data were obtained from hospital records. Results: Of 150 isolates, 130 (86.7%) represented infection and 20 (13.3%) colonization. Among 130 infected patients, skin and soft-tissue infections predominated (61.5%), followed by vaginitis (12.3%) and osteomyelitis (8.5%). Extravaginal isolates accounted for 75.3% of all isolates, while noninvasive infections constituted 70.8% of infections. Diabetes mellitus was the most common comorbidity (52.0%). Resistance was highest to tetracycline (32.0%), erythromycin (22.7%), benzylpenicillin (20.7%), and clindamycin (18.0%). Invasive disease was associated with higher mortality (OR: 5.56; 95% CI: 1.31-23.56; P =0.018). Conclusion: GBS predominantly affected adults with comorbidities, particularly diabetes (52.0%). Extravaginal (75.3%) and noninvasive infections (70.8%) predominated, whereas invasive disease (29.2%) accounted for 66.7% of deaths. Notable resistance to tetracycline, erythromycin, benzylpenicillin, and clindamycin in this study highlights the need for surveillance and antimicrobial stewardship.