[An epidemiological study of group A, B, C, and G hemolytic streptococci isolated from elementary school children in the recent 12 years. Part I. Isolation trends. Streptococcal Diseases Study Group].

During a 12-years period between September, 1980 and November, 1992, hemolytic streptococci (group A, B, C, & G) in throats of healthy school children in Osaka were examined every other month. The results were summarized as follows. 1. 5,023 strains of hemolytic streptococci were detected from 11,647 specimens, 43.1%. Among them, 2,395 strains (20.6%) belonged to group A, 1,647 (14.4%) to group B, 767 (6.6%) to group G and 187 (1.6%) to group C. 2. In the first half of the research, group A streptococci were detected predominantly and the last half, group B generally. Both this lower rate of group A to the total strains (47.7%) and this higher rate of group B (33.3%) were due to the small number of lower school grade children from whom group A streptococci are often detected and also due to application of the selective enrichment medium. 3. Group A streptococci were classified T-type. The most common serotype was T-1, and 638 strains (26.6%) were detected, followed by T-12, 377 (15.7%), T-6, 210 (8.8%) and T-13, 203 (8.5%). The dominant serotype was exchanged annually, but only T-1 was the most common serotype for 4 years (1983-1986). 4. In group B, the most common serotype was Ia, and 524 strains (31.3%) were detected, followed by III, 417 (24.9%), Ib, 164 (9.8%), III/R, 130 (7.8%) and Ia/c 122 (7.3%). Annual changes of serotype were as follows; Ia was dominant from 1980 to 1988, III from 1989 to 1990 and NT6 in 1991-1992 generally.