The Topic of This Month Vol.17 No.6 (No.196)

Shigellosis, Japan, 1993-1995

Dysentery patients reported in compliance with the Communicable Diseases Prevention Law totaled 1,120 and 1,042 in 1993 and 1994, respectively, of which shigellosis patients in the respective years numbered 968 (86%) and 892 (86%) and amoebic dysentery ones 152 (14%) and 150 (14%). In Fig. 1 shown are the numbers of shigellosis patients according to the estimated places of infection. In 1993 and 1994, domestically infected cases accounted for 39% and 23%, respectively. Cases having acquired infection in the Asian areas accounted for the majority as usual, being 52% in 1993 and 66% in 1994. The estimated places of infection were India, Indonesia, and Thailand in order of importance in both years, but the order was not necessarily the same as that in the preceding years. With respect to the age distribution of shigellosis cases, 20-29 years' patients accounted for about half, followed by 30-39 years' and 0-9 years' ones, each group accounting for 10-odd percent.

According to the reports of monthly isolation of Shigella by prefectural and municipal public health institutes, the peaks are seen in April and December in 1994 and in November in 1995. These peaks coincide with those of Shigella sonnei (Fig. 2).

The shigellosis outbreaks reported in IASR in 1994 and 1995 counted 10, of which five were caused by S. sonnei (Table 1).

The principal clinical symptoms of shigellosis patients admitted to the infectious diseases hospitals according to domestic and imported ones are shown in Table 2. The main symptoms were abdominal pain and watery diarrhea in every patient.

As Fig. 1 indicates, many of shigellosis patients having occurred in this country were imported ones returning from abroad.

The outbreaks of shigellosis of which details were reported in IASR recently, were as follows:

(1) This was an incident of shigellosis transmitted from a pet monkey to humans proved by epidemiological investigation and by clarification of the drug sensitivities of the isolates and identification of their plasmid profiles, pathogenic factors (see IASR, Vol. 15, No. 1).

(2) This was a familial infection. The index patient was a 7-year-old girl, who was diagnosed as septicemic shock and from whose stool specimens isolated was Shigella flexneri 2a on the 2nd day of illness. Subsequent epidemiological investigations found that her mother and grandmother also developed illness and the organisms of the same serovar were isolated from them. The source of infection, however, was not identified (see IASR, Vol. 15, No. 6).

(3) This was a domestic outbreak extending to three prefectures, Chiba, Saitama, and Ibaraki, where a total of 56 persons developed illness, 41 being genuine shigellosis and the other 15 suspected cases of shigellosis. S. sonnei was isolated as the agent. This outbreak extended to more than one prefecture; therefore, the subsequent epidemiological investigations was difficult (see IASR, Vol. 16, No. 4).

(4) This was the first incident of sporadic cases due to fluoroquinolone-resistant Shigella and the necessity of future monitoring of such organisms and of nationwide epidemiological investigations were pointed out(see IASR, Vol. 17, No. 3).

(5) This was an outbreak due to Shigella boydii having occurred among overseas travelers. Five of 18 participants of a group tour developed illness, but no secondary infection occurred among their family members. Intensification of hygienic education and guidance about imported infection increasing in association with the recent increase in overseas travelers to those who may be concerned is indicated (see incident No. 9 in Table 1 and IASR, Vol. 17, No. 4).

This report is based on the laboratory data submitted by prefectural/municipal public health institutes, quarantine stations, national/university hospitals and commercial diagnostic laboratories participating in the National Epidemiological Surveillance of Infectious Diseases. The data are compiled by the Infectious Agents Surveillance Center at the National Institute of Health, Japan.

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