Changes and changing concepts in the biology of group A streptococci and in the epidemiology of streptococcal infections.

Concepts of the cellular structure of group A streptococci have been modified by the recognition of surface fimbriae and by problems with the older view of a layered arrangement of cell wall components. Evidence of genetic drift of serologic types and of some increase in the prevalence of erythromycin-resistant strains has appeared. A curiois bimodal age distribution for streptococcal pharyngitis and an increase in the prevalence of non-group A strains has been detected. Despite repeated challenges, the value of throat cultures for confirming the possibility of streptococcal pharyngitis remains firmly established; throat cultures are superior to saliva cultures, which more frequently detect non-group A streptococci. Difficulties in detecting subclinical steptococcal infections and in defining streptococcal infection in children in endemic situations (particularly in separating true streptococcal infection from carriage of streptococci in individuals whose illness is due to some other agent) continue to present problems to clinicians and epidemiologists. The value of school culture surveys and of treatment of asymptomatic family contacts of cases remains uncertain. A 20% bacteriologic failure rate has been reported after intramuscular treatment with benzathine penicillin, but no in vitro evidence of resistance to penicillin has appeared. No adequate explanations are available for the decline in the problem of rheumatic fever in industrialized countries, for its increased recognition in tropical countries, for the failure of rheumatic fever to occur after streptococcal pyoderma, or for the emergence of group B Streptococcus as a predominant bacterial pathogen in newborn infants.