When food is incriminated as a source of EHEC infection and food poisoning is notified by a physician or admitted by the director of a health center, each local government will carry out investigations and notify the national government of the incident complying with the Food Sanitation Law.
Notified cases under the NESID: In compliance with the Infectious Diseases Control Law, 1,616 symptomatic and 1,370 asymptomatic new cases of EHEC infection, totaling at 2,986 cases (hereafter referred to as cases of EHEC infection), were reported in 2003 (Table 1). Asymptomatic carriers may sometimes be found incidentally at regular stool tests among food handlers and their employees, but are often found in an investigation of contact cases among family members and others after detection of the index case or investigations of common consumers of incriminated food and those who engaged in cooking in the incidents suspected of foodborne infection.
Small peaks were found in weekly reports of 2003 at the 23rd (June 8-14), the 29th (July 20-26) and the 35th (August 31- September 6) weeks. The largest peak used to be found in summer, however, in 2003, an increase was seen at the 39th week (September 29-October 4) (Fig. 1). These peaks reflect the outbreaks described later (see Table 3). The incidents by prefecture in 2003 count at 0.25-8.98 per 100,000 population; a considerable district difference can be seen (Fig. 2). Ishikawa Prefecture, where multiple outbreaks occurred, gave the largest number of cases (8.98), followed by Kumamoto (7.70) and Miyazaki Prefectures (6.17). In 2003, among cases of EHEC infection, 0-4 years old counted the largest in number, followed by 5-9 years. There were more males among those aged 0-19 years; and more females among those aged >=20 years. The rate of symptomatic patients was high among the younger generation and the aged in both males and females (58% of those aged =<19 years and 68% of those aged >=65 years), and below 50% of those aged 30s, 40s and 50s (Fig. 3). Among symptomatic patients, two cases, a girl aged six and her brother aged five, were dead at the time of reporting (see p. 143 of this issue).
EHEC isolation: Reports of EHEC isolation to the Infectious Disease Surveillance Center (IDSC), the National Institute of Infectious Diseases, detected by prefectural and municipal public health institutes (PHIs) counted at about 1,800 in 2002, which decreased to about 1,300 in 2003 (see p. 140 of this issue). The difference in number between the reports of EHEC isolation and cases of EHEC infection (Table 1) shows that a part of the information of the strains detected outside of PHIs does not reach PHIs by the current system.
The serotypes of EHEC isolates keep on involving O157 in about 70%, O26 in about 20%, and O111 in a few percent (see IASR, Vol. 17, No.1, Vol. 21, No.5, and Vol. 23, No. 6). Various other serotypes are being found, although in small number, and some strains, not identifiable by commercial antisera, produce Verocytotoxin (VT), therefore confirmation of VT is important for identification of EHEC (see p. 141 of this issue). As for the VT types (or VT genotypes) of EHEC isolates, VT1 & VT2 accounted for 60-70% of O157 since 2001 (68% in 2003). For O26 and O111, VT1 alone accounted for more than 80%. In 2003, hemolytic uremic syndrome (HUS) was reported in 17 of 1,293 cases giving EHEC (Table 2). O157 was detected in 11 of these cases (VT1 & 2 in four cases and VT2 in seven cases). O165 (VT2), O169 (VT2), O177 (VT1), and O untypableiUTj(VT1 & 2) each in one case and OUT (VT2) in two cases. The symptoms of 905 cases in which O157 was detected included bloody diarrhea in 31%, diarrhea in 47%, abdominal pain in 41%, fever in 17%, and no symptom in 38%.
Outbreaks: Among the outbreak incidents reported to IDSC in 2003, the number of those suspected to be foodborne infection, and involving more than 10 EHEC-positive cases, was three (Table 3). In an outbreak (No. 10), occurring at multiple kindergartens, an identical pattern was obtained from pulsed-field gel electrophoresis (PFGE) of O26 isolates from patients and the cause was ascribed to the food commonly served (see p. 149 of this issue). In an outbreak presumably caused by meals delivered to elderly people (No. 2), a fatal case was reported. In many incidents, the route of infection, whether it was person-to-person or foodborne infection, was not clarified. In 2003, outbreaks at nursery schools/kindergartens were counted still as many as six. For prevention of outbreaks due to person-to-person infection at such facilities as nursery schools, thorough daily education of staffs for hand washing (particularly after changing baby's diaper) and that of children also for hand-washing after defecation and before eating (see p. 148 of this issue) seem important. Also in summer, it is necessary to pay attention to sanitary guidance or control of paddling pools for children (see IASR, Vol. 24, No. 6). It is a characteristic feature of EHEC infection that secondary infection to family members often occurs (Table 3). To prevent expansion and extension of outbreaks, thorough education of parents for prevention of secondary infection seems necessary.
In 2003, incidents of EHEC food poisoning reported from local governments in compliance with the Food Sanitation law counted at 12, involving 184 cases.
Pulse-Net Japan: At present, efforts are being made to rapidly find out diffuse outbreaks by a molecular EHEC surveillance system (Pulse-Net Japan) consisting of genotypes of isolates based on PFGE and epidemiological data. In 2003, although epidemiological linkage is unknown, at least seven clusters, each suspected to be a diffuse outbreak from the same PFGE pattern of O157 strains obtained in wide areas, were found (see p. 141 of this issue).
Update 2004: Cases of EHEC infection reported during the 1st-21st weeks of this year counted at 377. From early April through the middle of the month, infection with O157 showing the identical PFGE pattern was found in Okayama, Ishikawa, Fukui and Kagawa Prefectures, suggesting a diffuse outbreak (see p. 141 of this issue). Further increase in cases of EHEC infection is anticipated, requiring call for more attention.