1. Hepatitis A: Particularly many cases presumably acquired infection within Japan (domestic cases) in 1999 (Fig. 1). Cases having acquired infection presumably outside of Japan (imported cases) were on the increase during 2001 and 2002; the reports by September 2002 already outnumbered the yearly reports of 2001. The main region of infection of imported cases has been Asia. Infection in China has suddenly increased in 2002 (Table 1).
Age and gender: Males aged 20s-40s are notable among domestic cases, which increased in 1999 (Fig. 2). Imported cases of females at the age of 20s slightly increased in 2001, but no accumulation in a particularly suspected district of infection was seen. Most imported cases, which showed an increase in 2002, were males at the age of 30s-early 50s and were estimated to have been infected in China. The six cases reported as fulminant hepatitis were at the age of 40 to 64 years, and five of them were males.
Domestic cases: The incidence by prefecture is shown in Fig. 3. From soon after the enactment of the Infectious Diseases Control Law toward the 28th week of 1999, there were many reports of cases in such large cities as Tokyo, Osaka, Kyoto and Hyogo. During the 47th week of 1999 through the 8th week of 2000, incidence was reported weekly consecutively in Tokushima and a total of 63 cases were accumulated. In addition, consecutive incidence was reported during the 36th to 44th weeks of 2000 with a total of 21 cases in Gifu and 15 cases in Kanagawa. In 2001, during the 12th to 25th weeks, reported were 25 cases in Gifu, 18 cases in Osaka, and 16 cases in Hyogo, and 18 cases during the 19th to 23rd weeks in Kanagawa, 23 cases during the 15th to 30th weeks in Fukuoka, 36 cases during the 17th to 32nd weeks and 13 cases during the 39th to 44th weeks in Tokyo. In 2002, reported were 17 cases in Chiba, 13 cases in Tokyo, and six cases in Shizuoka during the 2nd to 8th weeks, and 14 cases in Yamaguchi, 11 cases in Aichi, 14 cases in Miyagi, and 11 cases in Yamagata during the 11th and 16th weeks. During the 10th to 27th weeks, 57 cases were reported in Tokyo, 17 cases in Kanagawa, 12 cases in Saitama, and nine cases in Chiba; a total of 95 cases in four prefectures. Thus, by the end of September, domestic cases of comparative number as the preceding year were reported.
Suspected route of infection: Of 1,790 domestic cases diagnosed during April 1999-September 2002, 374 (81%) of 459 cases with suspected route of infection recorded were ascribed to consumption of fish and shellfish such as raw oysters, and 48 cases (10%) to the consumption of sushi. The followings are recent outbreaks from which hepatitis A virus (HAV) was detected and estimated to have been due to the same route of infection.
1) In December 2001, 22 of 57 persons who consumed purplish Washington clams at a restaurant in Hamamatsu developed diarrhea and emesis due to infection with Norwalk-like virus (NLV) and four of them developed hepatitis A one month later (see IASR, Vol. 23, No. 5).
2) In March 2002, 44 of 86 persons who partook of purplish Washington clams at a restaurant in Tokyo were assaulted by NLV food poisoning, and one month later, two of them developed hepatitis A. In addition, a restaurant worker and two other customers also developed hepatitis A (see p. 273 of this issue).
3) During September and November 2000, a total of 23 persons including the owner and four workers of a sushi bar, 15 customers who dined at this restaurant and three of their family members in Gifu were assaulted by hepatitis A (see IASR, Vol. 23, No. 6).
4) Twenty-two customers who consumed sushi at the same sushi bar in Tokyo and two workers of the restaurant developed hepatitis A in March 2002 (see p. 273 of this issue).
Prevention and control: The first and the second instances described above may have been due to food materials contaminated with HAV. A survey conducted by the Ministry of Health, Labour and Welfare (Nishio et al.) detected HAV by RT-PCR in three (two clams and one purplish Washington clams) of 122 bivalves of China origin (see p. 274 of this issue). To identify the route of infection of hepatitis A, investigation of eating history of imported fish and shellfish is necessary, and to prevent spreading infection due to imported food distributed widely, exhaustive early notification of cases and grasp of the information of epidemic status of hepatitis A in the production area are desired. As a basic principle of prevention of food poisoning, heating food sufficiently to the central part before consumption is important.
In the 3rd and 4th instances, cooks primarily infected with HAV contaminated foods, which caused spreading of infection to customers. HAV is excreted before onset of disease; exhaustive hygienic control such as constant hand washing by the cooks is essential. Familial infection may often occur by person-to-person transmission, which may sometimes cause spreading of infection in the premises of a facility (see IASR, Vol. 18, No. 10). Hepatitis A can be prevented by vaccination; those who are over 16 years may be vaccinated voluntarily in Japan. Vaccination is desired not only to prevent infection of those who are traveling to a hepatitis A-epidemic area, but also to prevent the spreading of infection within a facility where infection has occurred.
2. Hepatitis E: At present, laboratory confirmation of hepatitis E is possible by detection of HEV gene by RT-PCR or by detection of IgM antibody by ELISA (see p. 275 of this issue). The NESID received seven reports of hepatitis E during April 1999-September 2002. Of these, HEV infection was confirmed in four cases; two were by gene detection by RT-PCR and the other two by antibody detection by ELISA. The confirmed cases were males at the age of 20s and 50s and their estimated districts of infection were overseas in three cases (China, India & Nepal, and India) and one within Japan. It took many days from their first medical examination to diagnosis (17 to 37 days).
The rate of anti-HEV IgG-antibody positives determined with the sera from healthy individuals in Japan collected in 1993 was 5.4% (49/900); the rate of those younger than 20s was very low, being 0.4%, and subsequently, the more advanced was the age, the higher was the rate, namely 6.2% for 30s, 16% for 40s, and 23% for 50s (see Fig. 4 and p. 275 of this issue). Besides, a variety of animal species have been shown to be susceptible to HEV, and in the recent investigation of Japanese pigs, HEV was detected from two of 73 pigs at the age of 60 days and from one of 22 pigs at the age of 90 days (BBRC, 289: 929-936, 2001). Research in development of hepatitis E vaccine is under progress at present (see p. 275 of this issue).