The Topic of This Month Vol.18 No.2(No.204)

Streptococcal infections in Japan, 1995

Of various pathological changes brought about by hemolytic streptococcal infection, mainly pharyngitis due to group A Streptococcus is reported to the National Epidemiological Surveillance of Infectious Diseases (NESID). The reports of the incidence furnished by sentinel clinics totaled 80,095 in 1994 and 60,007 in 1995. The yearly reports on the incidence per sentinel clinic were the fewest in 1987, being 21.1, and thereafter continuously increased, reaching 27.7 in 1991, 28.3 in 1992 and 29.0 in 1993. The largest number, 33.0, was attained in 1994, and then it decreased to 24.6 in 1995. The trend in the weekly reports of the incidence per sentinel clinic shows the highest incidence ever encountered after the start of NESID during the period from the latter half of 1993 to the early half of 1994, changing the customary "trimodal incidence pattern, with reiteration of high-low-low peaks"; high incidence during October-December followed by low incidence during January-March and May-July. The customary incidence pattern was restored in 1995 (Fig. 1).

IASR collects information on isolation of pathogens by the source of specimens from general clinical institutions after January 1990. In 1994, reports on isolation of group A Streptococcus from nasopharyngeal sources numbered 13,055 and those from respiratory secretions (sputum, tracheal aspirates, and specimens of the lower respiratory tract) 820. The corresponding figures in 1995 were 7,704 and 676, respectively. As was the case with the reports of incidence, those on isolation, which were increasing after 1990, turned to decreasing for the first time in 1995.

The reports on isolation of group A Streptococcus by the T serotype furnished from prefectural and municipal public health institutes (PHIs) to IASR during the period from January 1988 through December 1995 are illustrated in Fig. 2. The total instances of isolation formed a trimodal pattern as did the reports of incidence NESID received (Fig. 1).

The yearly reports on T serotyping of group A Streptococcus numbered 1,271-2,556 during the period from 1988 to 1995 (Table 1). The T serotypes frequently detected in every year were T1, T4 and T12; these three serotypes accounted for more than 50% of the isolates reported each year. The yearly frequencies of isolation of these serotypes highlight the peaks of isolation of the T1 serotype in 1988 and 1992, those of T4 in 1989 and 1991, and those of T12 in 1990 and 1991. The T12 serotype tended to increase after 1992, but no sudden change was seen. On the other hand, a suddenly increased percentage of reports on isolation of T3 is seen from 1% in 1991 to 11% in 1993. In contrast, the percentage of the reports on isolation of T6 suddenly decreased from 11% in 1989 to 2% in 1991. The reports on isolation of T28 gradually increased from 5% in 1993 to 12% in 1995. TB3264 increased slightly from 7% in 1992 to 10% in 1993, but was kept on a 7-8% level during 1994-1995.

Severe invasive group A streptococcal infections: In Japan as well as European and American countries in recent years, severe invasive group A streptococcal infections (TSLS: toxic shock-like syndrome) due to so-called "flesh-eating bacteria" has become a problem. Attempts have been made to explain the emergence of TSLS by some change in immune status of the host or that in the virulence factor of the bacterial agent, but no decisive conclusion has been drawn.

In response to the Japanese first report of a case of TSLS in 1992, surveillance for TSLS was started (see p. 27 of this issue with respect to the criteria for diagnosis recommended by the Centers for Disease Control and Prevention (CDC), USA, with slight modification in Japan). Patients of TSLS reported to NIH through PHIs numbered 13 in 1994 (three in Chiba, two in Hiroshima, and one each in Yamagata, Kanagawa, Shizuoka, Hyogo, Tottori, Kochi, Kumamoto and Oita Prefectures) and 12 in 1995 (two each in Chiba, Shizuoka and Tokushima, and one each in Akita, Aichi, Nara, Kochi, Saga and Miyazaki Prefectures). The T and M serotyping of 29 isolates having caused TSLS and sent to NIH after 1992 (the mean age of the source patients of these isolates was 48 years) found that eight were T1 (M1) and other 12 were T3 (M3). These two serotypes accounted for 69% of all the isolates (see Y. Inagaki, T. Konda, et al., Epidemiol. Infect., in press). The results agree with the report from CDC in 1990 stating that serotypes M1 and M3 accounted for nearly 80% of the strains causing TSLS in USA.

The main T serotypes causing group A streptococcal infections have been T1, T4, and T12 as described above, but these are not necessarily the main serotypes causing TSLS. With the sudden increase in the isolation of T3 serotype in 1993, cases of TSLS due to T3 serotype tended to increase. More detailed investigations seem warranted to clarify the cause-and-effect relationship.

Update: According to NESID, reports on cases of streptococcal infections largely increased during October-December 1996. Cases per sentinel clinic exceeded 1.00 in the 48th week (November 24-30) and it became 1.13 in the 50th week (December 8-14). The figures surpass those in the corresponding periods in the preceding two years and are next highest after those in 1993 (Fig. 1).

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