The total of 15 times throat cultures and 3 times blooding were performed on 12, 988 healthy school children, 97% of the registered, at two primary school at Nikko City, Tochigi Prefecture, for the period of January 1973 to October 1977. The isolated Beta-streptococci were grouped and T-typed serologically and Anti-streptolysin 0 titer was examined. Some scarlet fever and acute glomerulonephritis patients were observed during the corse of investigation.
The results obtained were as follows;
1) Positive rate of beta streptococci carriers was higher in winter time and lower in summer time, 42.6% at the highest and 10.9% at the lowest. The isolated beta streptococci belonged to group A as much 82.0%, B 4.0%, C 3.5% and G 10.0%.
2) Most prevalent T-type of group A belonged T-1, T-4 and T-12, showing the same T-type pattern as that reported on the patients in the whole country.
3) Distribution of T-type of isolated strains was different in each school and class, suggesting the important role of the class room.
4) Prevalent pattern of T-12 during the corse of investigation were different from those of T-1 and T-4.
5) The carrier rate of scarlet fever and acute glomerulonephritis patients was rather low compared to the non-attacked children.
6) Carrier state of the same T-type does not necessary stimulate the elevation of ASO titer, but new carrier state or change in T-type of carrying streptococci served to-stimulate ASO.
7) It seems that the prevalent T-type among healthy carrier in non-epidemic period would not be the prevalent type in the following epidemic period.