Factors associated with Group A Streptococcus emm type diversification in a large urban setting in Brazil: a cross-sectional study

Children 3-15 years of age were consecutively recruited from slum and non-slum pediatric outpatient clinics between April-October, 2008. Throat cultures were performed and data intake forms were completed. GAS isolates were typed by emm sequencing.From 2194 children, 254 (12%) GAS isolates were obtained. Of 238 GAS isolates that were emm-typed, 61 unique emm types were identified. Simpson's diversity index of the emm types was higher among isolates from slum children [97% (96%-98%)] than those of non-slum children [92% (89%-96%)]. Two emm types (66.0, 12.0) were more frequently isolated from children with sore throat (p < 0.05), and one emm type (27G.0) demonstrated a protective effect.The emm type diversity from children attending slum clinics resembled the emm diversity of low income countries rather than that of children attending a non-slum clinic in the same city. Local factors, such as crowding, may enhance the frequency of GAS transmission and horizontal gene transfers that contribute to increased strain diversity in the slums. GAS vaccine coverage and control of GAS infections will need to take these local factors and strain differences into consideration.Group A Streptococcus (Streptococcus pyogenes; GAS) causes a wide spectrum of diseases, including pharyngitis and pyoderma to more severe diseases such as toxic shock syndrome, necrotizing fasciitis, glomerulonephritis and rheumatic heart disease (RHD) [1]. Children are the major reservoir of GAS [2]. The highest prevalence of GAS infections and their complications are found in developing countries [3].GAS strain typing is frequently used to characterize the epidemiology and pathogenesis of GAS infections. The most common target of typing methods is the M protein, which is a cell surface virulence factor serving as a target of the immune response to GAS that confers type-specific resistance. A sequence-based typing system called emm sequence typing, based on the N-terminus hypervariable region (5') of the M