Natural history of impetigo. I. Site sequence of acquisition and familial patterns of spread of cutaneous streptococci.

The appearance on and spread of Group A streptococci among different body sites in relationship to the development of impetigo were studied prospectively in 31 children in five families. During July and August 1969 intensive clinical, bacteriological, and serological observations were made, including cultures taken at least every other day. In individual children, site sequence of spread of Group A streptococci was from normal skin to lesions and finally to respiratory tract. Streptococci were recovered from normal skin before development of lesions (mean interval of 10 days) in 74% of episodes. Recovery of streptococci from nose and throat followed (by means of 14 and 20 days, respectively) skin acquisition of streptococci (97% of episodes) and lesions (74% of episodes).Distribution of positive normal skin sites among wrist, ankle, and back was similar (28-37%) although 62% of lesions were on the legs. Recovery of a serotype from normal skin was associated with a high risk (76%) of subsequent development of lesions due to that type. New streptococcal serotypes usually entered a family during the peak or decline of a preceding serotoype with a tendency of one to predominate. Among family members the mean interval from index to secondary skin acquisition of streptococci was 4.8 days, but 21 days elapsed from first appearance to last acquisition of skin disease. In the population as a whole, streptococci were recovered in high frequency from normal skin before the increase in prevalence of lesions and also later in the fall when cutaneous infections were absent.