The Topic of This Month Vol. 31, No. 6 (No. 364)
Prefectural and municipal public health institutes (PHIs) conduct isolation of EHEC, serotyping, and VT typing, while the Department of Bacteriology, National Institute of Infectious Diseases (NIID), conducts molecular epidemiological analysis, whose result is made available through the PulseNet Japan (see p. 155 of this issue).
Cases notified under NESID: In 2009, total 3,878 EHEC infections, 2,601 symptomatic and 1,277 asymptomatic were reported (Table 1). As in previous years, there was a large peak in summer (Fig. 1). Incidence (cases per 100,000 population) was highest in Saga Prefecture (22.06) followed by Oita (9.20) and Ishikawa (8.06) (Fig. 2, left); prefectures with higher incidence in 2005-2008 tended to be so in 2009. As in previous years, incidence of EHEC infection was highest among the age group of 0-4 years followed by 5-9 year age group (Fig. 3). When different prefectures were compared for EHEC incidence, Saga and Oita Prefectures (see p. 162 of this issue), which had EHEC outbreaks in nursery schools, were the highest (Fig. 2, right).
In the present surveillance system, when a patient is found, the surrounding population is investigated for further possible infections. Under investigations so conducted, the proportion of asymptomatic infection is continuously higher in those aged 30-59 years and lower in younger or older age groups in recent years (Fig. 3). Total 83 hemolytic uremic syndrome (HUS) cases, corresponding to 3.2% of symptomatic cases, were reported in 2009 (see p. 170 of this issue). Among 55 cases from which EHEC were isolated, 91% of the isolates were O157; among them 95% produced VT2 with or without VT1. Three fatal cases, older than 80 years, were not associated with HUS.
Isolation of EHEC: In 2009, number of EHEC isolates that PHIs reported to the Infectious Disease Surveillance Center (IDSC), NIID, was 2,168, far less than the reported number of EHEC infection cases (Table 1). The discrepancy is due to the present situation where a substantial amount of the laboratory data obtained outside of PHIs does not reach NIID. The most frequent O-serotype had been O157, followed by O26 and O111. However in 2009, the order was O157 (64%), O26 (23%), and O121 (3.2%), and O111 (2.6%) was next to O121 (see Table in page 154). Since 2005, seven additional antisera against frequently encountered serotypes have become commercially available (see p. 168 of this issue). Many other serotypes are increasingly obtained in recent years (http://idsc.nih.go.jp/iasr/virus/bacteria-e.html). For identification of EHEC, confirmation of VT is essential. In 2009, 64% of the O157 isolates produced both VT1 and VT2 (53-68% in 1997-2008), while, among O26 and O111, 89% and 80% respectively produced VT1 alone.
In 2009, among 1,396 cases due to O157, clinical record was available for 1,327 cases. Major symptoms were diarrhea (58% of the cases), abdominal pain (56%), bloody diarrhea (42%), and fever (20%) (see Table in p. 154 of this issue).
Outbreaks and their prevention: In 2009, PHIs reported to IDSC 21 EHEC outbreaks, including ten outbreaks caused by O157. Among 14 outbreaks involving ten or more EHEC-positive cases (Table 2), five outbreaks were suspected to be food-borne, and seven were suspected for occurrence of person-to-person transmission. In 2009, 26 EHEC incidents involving 181 patients were reported by prefectures in compliance with the Food Sanitation Law (17 incidents and 115 patients in 2008).
In 2009, there were three diffuse outbreaks affecting geographically wide areas (Table 2); two were caused by beefsteak restaurant chains spreading all over Japan (see p. 156, 157&158 of this issue) and one by a yakiniku restaurant chain in the metropolitan area (see p. 159 of this issue). Initially some cases were reported as sporadic cases by different prefectures, but after PFGE analysis of the EHEC isolates, they could be identified as parts of either one of the three big outbreaks (see p. 155 of this issue). For detection and control of such diffuse outbreaks, it is important that local governments, PHIs and other parties involved, share epidemiological and genetic data. In April 16, 2010, MHLW issued an announcement “On countermeasures against diffuse and wide-ranged food poisoning caused by EHEC O157” (see p. 160 of this issue).
Foods contaminated with small number of EHEC can cause food-borne infection. Therefore, every people should observe the standard hygienic practices for preventing food poisoning. It is also important that raw or undercooked meat should not be given to younger children, elderly or immunocompromized persons in view of consequence of possible contamination of EHEC, Campylobacter or human hepatitis E virus (http://www.mhlw.go.jp/topics/syokuchu/03.html).
Similarly as Shigella , EHEC establishes infection even at minute doses and can spread from person to person rather easily. In 2009, there were nine EHEC outbreaks in nursery schools (Table 2). For preventing outbreaks in nursery schools or kindergartens, appropriate hygienic practice, such as routine hand washing and sanitary use of children's padding pools during summer, should be observed. Spread of infection within a family is not infrequent. Once a patient has appeared in a family, the health center should provide the family with thorough instructions necessary for preventing the secondary infections.
Update 2010: During weeks 1-19 of this year, 398 EHEC cases were reported (Table 1). As EHEC infection increases in summer, vigilance on this infection should be increased.
The statistics in this report are based on 1) the data concerning patients and laboratory findings obtained by the National Epidemiological Surveillance of Infectious Diseases undertaken in compliance with the Law Concerning the Prevention of Infectious Diseases and Medical Care for Patients of Infections, and 2) other data covering various aspects of infectious diseases. The prefectural and municipal health centers and public health institutes (PHIs), the Department of Food Safety, the Ministry of Health, Labour and Welfare, quarantine stations, and the Research Group for Enteric Infection in Japan, have provided the above data.
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