Follow-up study of pharyngeal carriers of beta-hemolytic streptococci among school children in Sapporo City during a period of 2 years and 5 months.

A total of 124 normal school children in three classes (aged 8 to 9) were examined for beta-hemolytic streptococci for 29 months from August 1977 to December 1979 be means of serial monthly throat cultures. No significant difference between the carrier rate of boys and that of girls was observed. Although no monthly variation of carrier rates appeared in class II, marked temporal increases of carrier rates appeared from June 1978 (in Class I) and from August 1978 (in class III) in August 1979. These periodical variations of carrier rates observed in this investigation do not coincide with the low-in summer and high-in winter seasonal variations which has generally been observed by many other investigators. The average values of carrier rates throughout the period of this investigation were 30.9, 29.7, and 24.5% in classes I, II, and III, respectively. The carrier rate of group A streptococci by month and by class showed some positive correlation with the carrier rate of total beta-hemolytic streptococci. T-type 4 and T-untypable strains were not identified up to a certain period; then each strain appeared at a given time during the course of our investigation in one class, spread to all three classes, and continued to be isolated until the end of this investigation. The origin of these type of strains could not be identified in this study. Of the children, 36 (29.0%) never became streptococcal carriers during the period of examination and 88 (71.0%) became streptococcal carriers at least one time during the 29 examinations; among these positive carriers, 29 children (23.0%) showed positive results in more than 50% of the examinations.