The Topic of This Month Vol. 32, No. 5 (No. 375)
Prefectural and municipal public health institutes (PHIs) conduct isolation of EHEC, serotyping, and VT typing, while the Department of Bacteriology I, National Institute of Infectious Diseases (NIID), conducts molecular epidemiological analysis, whose result is made available through the PulseNet Japan (see p. 128 of this issue).
Cases notified under NESID: In 2010, total 4,135 EHEC infections, 2,719 symptomatic and 1,416 asymptomatic, were reported (Table 1). As in previous years, there was a large peak in summer (Fig. 1). Incidence (cases/100,000 population) was highest in Mie Prefecture (18.72) followed by Iwate (10.15) and Saga (6.34) though it was variable depending upon the year and prefecture (Fig. 2, left panel; IASR 31: 152-153, 2010). In general, however, prefectures with higher incidence in 2006-2009 tended to be so in 2010. 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 (cases/100,000) in population under 4 years of age, Iwate, Nagano and Nara Prefectures were the highest (Fig. 2, right).
The surveillance conducted through active surveillance to the population surrounding the infected cases and periodical stool specimen check of persons engaged in food preparation revealed that the proportion of asymptomatic infection was high among 30-59 year olds while symptomatic cases were more frequent in young and old age groups (Fig. 3).
Total 92 hemolytic uremic syndrome (HUS) cases, corresponding to 3.4% of the all symptomatic EHEC cases, were reported in 2010 (see p. 141 of this issue). Among the bacteria isolated from 62 cases, 89% were O157 and 87% produced VT2 with or without VT1. Three of the five fatal cases were HUS cases (one 2-year-old male, one female in her 60's, and one male in his 70's).
Isolation of EHEC: In 2010, number of EHEC isolates that PHIs reported to the Infectious Disease Surveillance Center (IDSC), NIID, was 2,007, far less than the reported number of EHEC infection cases appearing in Table 1. The discrepancy is due to the present situation where only a small fraction of strains detected/isolated in medical facilities or commercial laboratories are sent to PHIs. The most frequent O-serogroup was O157 (69%), followed by O26 (17%) and O103 (3.1%) (see Table on page 127). To cope with expanding spectrum of commonly encountered serogroups (http://idsc.nih.go.jp/iasr/virus/bacteria-e.html), the presently available commercial kit contains additional seven diagnostic antisera since 2005. However, as serogrouping alone is insufficient for identification/confirmation of EHEC, VT should be confirmed in every case. In 2010, 71% of the O157 isolates produced both VT1 and VT2 (53-68% in 1997-2009), while, among O26 and O103, 91% and 100% respectively produced VT1 alone. Among 1,384 cases from whom O157 was isolated, clinical record was available for 1,354 cases. Major symptoms were diarrhea (57%), abdominal pain (56%), bloody diarrhea (41%), and fever (23%) (see Table on page 127).
Outbreaks: In 2010, PHIs reported to IDSC in NIID 27 EHEC outbreaks, including 16 outbreaks caused by O157. There were 13 outbreaks involving ten or more EHEC-positive cases (Table 2). Four of them were suspected to be foodborne, while eight were probably person-to-person transmission incidents (playing with water could have been additional transmission route in two of them). In 2010, 27 EHEC incidents involving 358 patients (bacteria isolation negative cases included) were reported by prefectures in compliance with the Food Sanitation Law (26 incidents and 181 patients in 2009).
In 2010, there were successive four food poisoning incidents in Nagoya City all caused by EHEC O157 and all related to consumption of raw beef liver (see p. 129 of this issue). During the same period, food poisonings also caused by EHEC O157 occurred in multiple grilled meat restaurants in Aichi Prefecture. The PFGE patterns that were identical and investigation of the marketing routes revealed that the apparent diffuse incidents were actually one food poisoning incident affecting the wide area. As exemplified by this incident, for minimizing the spread of EHEC, it is crucial to sense a potential large-scale food poisoning through the bacteriological and epidemiological investigation of apparently diffuse food poisoning cases and to share the data in real time among the PHIs and responsible local organizations (see p. 128 of this issue). In April 16, 2010, MHLW issued an announcement “On prevention of geographically widespread food poisoning caused by EHEC O157” (IASR 31: 160-161, 2010).
Prevention: Foods contaminated with small number of EHEC can cause foodborne infection. Therefore, observing the standard hygienic practices is crucial for preventing food poisoning. It is also important that younger children, elderly or persons with reduced resistance should not eat raw or undercooked meat (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 easily. In 2010, there were seven 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 childrenfs 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 2011: During weeks 1-16 of this year, 211 EHEC cases were reported (Table 1). In addition, four fatal cases occurred due to foodborne EHEC O111 (VT2) infection during weeks 17-18 (http://idsc.nih.go.jp/iasr/rapid/pr3762.html). As EHEC infection increases in summer, vigilance on this infection should be increased.
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