Contrasting molecular epidemiology of group A streptococci causing tropical and nontropical infections of the skin and throat

Disease caused by group A streptococci (GAS) in tropical regions often take s the form of impetigo, whereas pharyngitis tends to predominate in tempera te zones. GAS derived from asymptomatic throat infections and pyoderma lesi ons of rural Aboriginal Australians were evaluated for phylogenetic distant emm genes, which represent ecological markers for tissue site preference. On the basis of the percentage of total isolates from a given tissue, emm p attern A-C organisms exhibited a stronger predilection for the throat, wher eas pattern D organisms preferred the skin, Only 16% of isolates collected by active surveillance displayed pattern A-C, which reflects the low incide nce of oropharyngeal infection. Importantly, most (70%) pattern A-C organis ms were isolated from skin sores, despite their innate tendency to infect t he throat. Combined with findings from nontropical populations, analysis of the data supports the hypothesis that GAS tissue preferences are genetical ly predetermined and that host risk factors for infection strongly influenc e the differential reproduction of individual clones.