Group A streptococcus.

Group A streptococci (GAS) are gram positive cocci that can be divided into more than 100 M-serotypes or emm types based on their M proteins. Their virulence is related directly to the M protein on the cell surface that inhibits phagocytosis. Although it is more commonly thought of in the context of causing clinical illness, Streptococcus pyogenes can colonize the pharynx and skin. Infections due to GAS include pharyngitis, impetigo, ecthyma, erysipelas, and cellulitis. These infections, as well as the manifestations of invasive disease including streptococcal toxic shock syndrome and necrotizing fasciitis, will be reviewed in this article. Also included will be the nonsuppurative complications of GAS infections, acute rheumatic fever and post streptococcal glomerular nephritis. GAS is an important cause of infections in children in both the ambulatory and hospital settings. Current efforts aimed at the development of a vaccine are warranted but remain in preliminary stages at this time.