Acquisition of group A streptococcal M protein antibodies.

Seventy-five children who acquired positive throat cultures for Group A streptococci among 250 cultured weekly were studied during the school years 1972-1973 and 1973-1974 in order to investigate streptococcal M protein antibodies. Eleven (14.7%) of the children had strain-specific serum M protein antibodies at the time a positive throat culture was first detected or 6 weeks previously. Eight of 64 (12.5%) children acquired strain specific serum M protein antibodies within 6 weeks and another 6 of 46 (13%) did so within 1 year of infection. The presence of strain-specific serum M protein antibodies did not appear to be protective. One-third of the 75 children who acquired positive throat cultures had a significant rise in anti-streptolysin O or anti-hyaluronidase antibody titers. Among those who acquired Group A streptococci, 25 children had positive cultures on 7 or more culture dates.