Population-based study of invasive disease due to beta-hemolytic streptococci of groups other than A and B.

Background: Beta-hemolytic streptococci of groups other than A and B (NABS) are increasingly recognized as causes of clinically significant disease, but precise information about this heterogeneous group is lacking. We report the incidence of NABS infection and describe the epidemiologic and clinical characteristics.

Methods: Active, population-based surveillance for invasive NABS was performed over a 2-year period in the 8-county metropolitan Atlanta, Georgia, area and the 3-county San Francisco Bay, California, area. Clinical records were reviewed, and available isolates were sent to the Centers for Disease Control and Prevention (Atlanta) for additional microbiologic characterization. Incidences were calculated using year-appropriate US Census Bureau data.

Results: A total of 489 cases of invasive NABS infection were identified (3.2 cases per 100,000 population). The median age of patients was 55 years; 64% of patients were males, and 87% had underlying diseases. The incidence was higher among black persons than white persons (4.0 vs. 2.5 cases per 100,000 population; P < .01) and increased with age among all races. Infections were community acquired in 416 cases (85%). Among the 450 patients (94%) with NABS infection who were hospitalized, 55 (12%) died. Of 266 isolates (54%) speciated at the Centers for Disease Control and Prevention, 212 (80%) were Streptococcus dysgalactiae subspecies equisimilis; 46 (17%) were members of the Streptococcus anginosus group. S. dysgalactiae subspecies equisimilis primarily presented as skin and soft-tissue infection in older patients, whereas individuals with invasive S. anginosus group infections were more likely to be younger patients with intra-abdominal infections.

Conclusions: NABS comprise multiple distinct species that cause a significant number of community-acquired invasive infections. Clinical manifestations differ by species. Thus, speciation of invasive NABS may be warranted in clinical settings.