Children in M nursery school in Kurobe City, Toyama Prefecture, where a small epidemic of reumatic fever caused by an erythromycin-resistant M type 12 streptococcus of group A occurred from November to December in 1973, were followed up both bacteriologically and serologically for approximately 1 year after the epidemic.
1. The carrier rate of hemolytic streptococci in this population was dramatically decreased 6 months after the epidemic, no M type 12 streptococcus carriers being detected at this time (June, 1974). The rate, however, re-increased in November 1974, 1 year after the epidemic, and the numbers of M type 12 streptococcus carriers outnumbered those in the epidemic period.
2. The individual carrier state of M type 12 strains between the 3rd and the 4th follow-up examinations (November 26, 1974 and January 16, 1975 respectively) was mostly unchanged, indicating the sedentariness of this type in the population of M nursery school.
3. Among the individuals who possessed the ASO antibody titer of 333 or more when the epidemic occurred, the average antibody titer decreased by 3 dilution tubes after 6 months and by 1 tube after another 6 months. Two cases of fresh streptococcal infection were suspected by a significant increase in ASO antibody titer during the follow-up examination period, one being a new carrier of M type 12 strain in the winter 1 year after the epidemic.
