Asymptomatic epidemic acquisition of group A Streptococcus: antibody response to extracellular and type-specific antigens.

The antibody response of 40 institutionalized children involved in an epidemic associated with asymptomatic pharyngeal acquisition of a group A, M-11, T-11 typeable Streptococcus was studied. Titers of antibody to streptolysin O and to deoxyribonuclease B determined in sera collected from patients within two weeks of positive throat cultures were significantly higher than those in sera of controls (P smaller than 0.001). However, there was no rise in antibody titers in sera obtained from these patients after an interval of three weeks. Type-specific antibody to the group A Streptococcus (type M-11) was assayed in the sera of 24 patients. No detectable antibody activity was found either in the initial sera or in sera collected eight months after the epidemic. Thus, the asymptomatic nature of this epidemic could not be attributed to the presence of detectable type-specific antibody in this population at the time of the epidemic. These observations suggest that asymptomatic pharyngeal acquisition of group A Streptococcus may occur in epidemic fashion in certain populations and may not be associated with evidence of an antibody response to the streptococcal organism.