A Retrospective National Study on Colonization Rate and Antimicrobial Susceptibility of Streptococcus agalactiae in Pregnant Korean Women, 2018–2020

Purpose: The prevalence of Group B Streptococcus (GBS) colonization in pregnant Korean women is increasing; however, nationwide studies are lacking. Therefore, we aimed to analyze regional colonization rates and antimicrobial susceptibility for GBS in pregnant Korean women through a nationwide survey. Materials and Methods: From January 2018 to December 2020, data from the Seoul Clinical Laboratories on vaginal swab cultures were retrospectively analyzed to detect maternal GBS carriers. Each swab specimen was inoculated onto a 5% blood agar plate and incubated at 35°C–37°C in a 5% CO₂ incubator for 24 h. GBS isolates were identified using a Microflex MALDI Biotyper. Antimicrobial susceptibility tests were performed using the Vitek 2 automated system. Results: The overall nationwide GBS colonization rate in pregnant Korean women was found to be 10.6% (3578/33721). The maternal GBS colonization rates ranged from 10.5%–10.8% over the 3-year study period. The GBS colonization rates by province, in descending order, were as follows: Jeolla-do, 13.2%; Gangwon-do, 12.0%; Chungcheong-do, 11.8%; Gyeonggi-do, 11.3%; Seoul, 10.2%; and Gyeongsang-do, 9.6%. During the study period, the resistance rates against chloramphenicol, levofloxacin, clindamy-cin, erythromycin, and tetracycline were 2.6%–2.7%, 18.2%–19.6%, 33.4%–35.7%, 35.6%–36.8%, and 50.5%–53.3%, respectively. Conclusion: In pregnant Korean women, GBS colonization rates were in the range of 9.6%–13.2%, with Gyeongsang-do being the lowest and Jeolla-do the highest. The resistance rate against clindamycin was high (33.4%–35.7%). GBS colonization rates during pregnancy should be studied nationwide according to the Centers for Disease Control and Prevention-recommended guidelines with periodic antimicrobial resistance monitoring.