Epidemiology of Streptococcus dysgalactiae subsp. equisimilis in tropical communities, Northern Australia.

Streptococcus dysgalactiae subsp. equisimilis (groups C and G streptococci [GCS/GGS]) is an increasingly recognized human pathogen, although it may follow indirect pathways. Prospective surveillance of selected households in 3 remote Aboriginal communities in Australia provided 337 GCS/GGS isolates that were emm sequence-typed. Lancefield group C isolates (GCS) were localized to specific households and group G isolates (GGS) were more evenly distributed. GCS/GGS was more frequently recovered from the throat than group A streptococci (GAS [S. pyogenes]) but rarely recovered from skin sores, and then only with Staphylococcus aureus or GAS. Symptomatic GGS/GGC pharyngitis was also rare. Specific emm sequence types of GCS/GGS did not appear to cycle through the communities (sequential strain replacement) in a manner suggesting acquisition of type-specific immunity. These communities already have high levels of streptococcal and poststreptococcal disease. GCS/GGS may increase in importance as it acquires key virulence factors from GAS by lateral gene transfer.