Streptococcal infections that fail to cause recurrences of rheumatic fever.

Prospective studies of recurrences of streptoccal infection and acute rheumatic fever were conducted among patients attending the acute rheumatic fever prophylaxis clinic (City of Memphis Hospitals, Memphis, Tennessee) between 1965 and 1972. The patient population consisted of 124 rheumatic children and adults, two-thirds of whom had evidence of rheumatic heart disease. A total of 104 immunologically documented streptococcal infections occurred during 235 patient-years of follow-up (44.3 infections per 100 patient-years) without a single recurrence of rheumatic fever. Immune responses tended to be modest, and 80% of the infections were subclinical. The majority of our group A streptococcal isolates were obtained from routine cultures of specimens from asymptomatic individuals. Many of these strains were "pyoderma" serotypes, whereas others exhibited a characteristic (production of opacity factor) recently reported to be associated with decreased immunogenicity. Several factors may have contributed to the low recurrence rate of acute rheumatic fever, including the age range of the population under study and immunologically significant infections with strains of Streptococcus that were not group A, but a major reason may be the possibility that the group A strains prevalent in this population have diminished rheumatogenic potential.