Evolving Antibiotic Resistance in Group B Streptococci Causing Invasive Infant Disease: 1970–2021

Background We sought to define the frequency of antibiotic resistance over time in a collection of invasive GBS isolates derived from infant early-onset disease (EOD), late-onset disease (LOD), and late-late onset disease (LLOD). Methods A multicenter retrospective review of infants born from 1970 to 2021 with GBS isolated from blood, cerebrospinal fluid, synovial fluid, cellulitis, or bone. All isolates were serotyped and antimicrobial susceptibility testing performed using disk diffusion. Results The most common serotypes in our 2017 isolates were III ( n = 1112, 55.1%), Ia ( n = 445, 22%), Ib ( n = 182, 9%) and II ( n = 146, 7.2%). A total of 945 (46.8%) isolates were from infants with EOD, 976 (48.3%) from LOD, and 96 (4.75%) from LLOD. All isolates were penicillin-susceptible. Compared to strains isolated <2000, strains isolated ≥2000 showed significantly greater frequency of erythromycin (4.0% to 32.3%, P < 0.0001) and clindamycin (1.5% to 17.5%, P < 0.0001) resistance. Year of isolation (≥2000) and serotype V were significantly associated with erythromycin and/or clindamycin resistance. Conclusions We document a rapid and significant increase in clindamycin and erythromycin resistance. As clindamycin may be considered in severely penicillin-allergic women needing GBS intrapartum prophylaxis, obstetricians, pediatricians, and neonatologist should be aware of this disturbing trend. Impact Group B streptococcal strains isolated from infants with invasive infection have become more resistant to second-line antibiotics over time. In this epidemiologic study of 2017 group B streptococci isolated from 1970 to 2021, penicillin susceptibility remained uniform; however, resistance to erythromycin and clindamycin increased significantly over time across all capsular serotypes. Clindamycin resistance exceeded 20% by 2010 in most serotypes. While penicillin remains the treatment of choice for group B streptococcal infant disease, pediatricians and neonatologists should be aware of the high prevalence of resistance to clindamycin, a recommended alternative drug used for intrapartum-antibiotic prophylaxis in penicillin-allergic women.