Objective. A 4-year longitudinal study of school-aged children was conducted to describe the clinical characteristics and epidemiologic features of infections with group A streptococci (GAS).

Methods. Between 1998 and 2002, surveillance throat cultures were performed twice per month (October to May) for a cohort of elementary school children in Pittsburgh, Pennsylvania. In addition, throat cultures were obtained during any respiratory illness. Erythromycin and clindamycin susceptibility testing was performed for all isolates. Molecular typing was performed with field-inversion gel electrophoresis. Representative isolates from each field-inversion gel electrophoresis group were emm typed. Strict definitions were used to characterize each GAS infection. Children were classified into 4 categories each year, ie, single episode, recurrent episodes, carriers of GAS, and no infections.

Results. A total of 48 to 100 children per year were studied for 4 years; 61 (49%) were male. The mean age was 9.6 years (range: 5–15 years). A total of 5658 throat cultures were performed; 878 (15.5%) were positive for GAS. Antimicrobial agents were used to treat 209 episodes of infection. Thirteen emm types were observed during the 4-year period. GAS were isolated most often from children who were carriers; isolates from single episodes were next most common. Children carried a single emm type for a mean of 10.8 weeks (range: 3–34 weeks). Carriers were likely to be classified again as carriers in subsequent years and frequently switched emm types. Sixty-two percent of the children had ≥1 year with no infections.

Conclusions. GAS infections are common among school-aged children. The majority of positive throat cultures observed in this longitudinal study were obtained from children who were carriers of GAS. Carriers switched emm types but tended to become carriers repeatedly during the study. Practitioners should consider treating children known to be GAS carriers when they develop a new illness that is consistent with streptococcal pharyngitis, because they may acquire new emm types and be at risk for rheumatic heart disease.

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