Serotype Distribution and Antimicrobial Resistance of Streptococcus agalactiae Isolates in Nonpregnant Adults with Streptococcal Toxic Shock Syndrome in Japan in 2014 to 2021

The incidence of streptococcal toxic shock syndrome (STSS) due to group B Streptococcus (GBS) has been increasing annually in Japan and is becoming a serious challenge. Furthermore, in recent years, penicillin- or clindamycin-resistant strains used in treating streptococcal toxic shock syndrome have been reported. However, no report analyzed >100 isolates of group B Streptococcus causing streptococcal toxic shock syndrome. Therefore, we aimed to perform serotyping and antimicrobial susceptibility testing of 268 isolated group B Streptococcus strains from streptococcal toxic shock syndrome cases involving nonpregnant adult patients in Japan between 2014 and 2021. The most prevalent serotype was Ib, followed by serotypes V, III, and Ia. Seven isolates were resistant to penicillin G, and 17.9% (48 isolates) were resistant to clindamycin. Of the penicillin-resistant group B Streptococcus isolates, 71.4% (5 isolates) were clindamycin resistant. In addition, group B Streptococcus strains resistant to penicillin and clindamycin were isolated from patients with streptococcal toxic shock syndrome. Therefore, before these strains become prevalent, introduction of the group B Streptococcus vaccine is essential for disease prevention. IMPORTANCE Group B Streptococcus (GBS) has been increasingly associated with invasive disease in nonpregnant adults. Such infections are responsible for substantial morbidity and mortality, particularly in individuals with underlying chronic conditions. Streptococcal toxic shock syndrome (STSS) is a severe invasive infection characterized by the sudden onset of shock, multiorgan failure, and high mortality. In this study, we assessed 268 GBS-related STSS cases in nonpregnant adults in Japan between 2014 and 2021. Serotype Ib was the most prevalent, followed by serotypes V, III, and Ia, which were identified in more than 80% of STSS isolates. We found that 48 clindamycin-resistant strains and 7 penicillin G-resistant strains were isolated between 2014 and 2021. We believe that our study makes a significant contribution to the literature because we show that the GBS vaccine, particularly the hexavalent conjugate vaccine, is important to reduce the number of patients with STSS.