Group B Streptococcus infections in non-pregnant adults: the role of immunosuppression

Abstract

Background: Group B Streptococcus (GBS) is a known causative pathogen of neonatal sepsis, but the epidemiology in non-pregnant adults is less studied.

Methods: Retrospective case-control and cohort analyses of risk factors and outcomes of GBS infections among non-pregnant adults were conducted at the Detroit Medical Center from January 2005 to May 2010. Uninfected controls were matched to cases in a 3:1 ratio. Data were obtained from charts and pharmacy records. Identification of the bacteria and antimicrobial susceptibility testing were determined by MicroScan. Cox regression was used for matched multivariate analyses.

Results: Thirty-two patients with GBS infections were identified and were matched and compared to 96 controls. Compared to controls, patients with GBS infection were significantly younger. Immunosuppression, attributable mainly to neutropenia and recent use of glucocorticoids, was an independent predictor for GBS infection (odds ratio 2.7, p=0.03). Nine (28%) of the patients with GBS infection had bacteriological failure despite the administration of appropriate antimicrobial therapy. Of the 10 patients with bloodstream infections (BSI), three had endocarditis and four had central nervous system (CNS) infections. During the study period the incidence of infections decreased, but the rates of resistance to erythromycin and clindamycin increased.

Conclusions: GBS, previously considered a genitourinary pathogen, has emerged as a non-nosocomial opportunistic pathogen causing BSI, endocarditis, and CNS infections. Immunosuppression, particularly transient immunosuppressed states, was an independent predictor for GBS BSI. Resistance rates to macrolides and clindamycin continue to increase, and should be closely monitored.