The dynamics of streptococcal infections in a defined population of children: serotypes associated with skin and respiratory infections.

Serial observations including cultures of the upper respiratory tract and of infected skin lesions and streptococcal antibody determinations were made over a two-year period in a semi-closed population of children between 10 months and 15 years of age. There was a high prevalence of group A streptococci in nose and throat cultures and of skin lesions containing these organisms. Almost 90% of the study population developed streptococcal impetigo during the study period. A slightly higher proportion of males than females developed skin infection but there was no relationship to age. Impetigo was observed throughout the calendar year, exceeding 12% of child-visits in one winter month, but was generally more common in the summer and fall. Conversely, group A streptococci were more often isolated from nose and throat cultures in the winter months. The increase in recovery of streptococci from nose and throat cultures lagged behind the increase in streptococcal impetigo and continued into the winter months, when the prevalence of impetigo had declined. Calculation of ratios for individual streptococcal serotypes isolated from different body sites revealed a clear cut distinction between "respiratory" and "impetigo" serotypes, with respect to both prevalence and acquisition rates. Respiratory serotypes were more commonly isolated in the winter and impetigo serotypes in the summer and fall. Significant antibody responses to extracellular antigens of the streptococcus were documented for pharyngeal acquisitions of both impetigo and respiratory serotypes and for skin lesions associated with impetigo serotypes. Group A streptococcal serotypes may be divided into three categories on the basis of their human pathogenicity for body sites: some with the potential for respiratory infection, others with the potential for skin infection and a few unusual serotypes with the potential for infecting both sites.