Type-specific immunity and pharyngeal acquisition of group A Streptococcus.

A prospective study of spread of M-type 1, 2, 13, 14, 25 and 60 group A Streptococcus in 64 families in Qalyub, Egypt, in 1972-1974 showed that type-specific serum bactericidal antibody does not protect against pharyngeal acquisition of homologous organisms. The presence of type-specific antibody also does not appear to affect duration of carriage of the organism. Type-specific immunity must be mediated in another way, such as by local antibody or trough prevention of infection (as evidenced by a host response) following acquisition. This study also confirms the observations of others that administration of penicillin lowers the probability that a person who acquires group A Streptococcus will develop type-specific antibody.