An Epidemiological Consideration On the Recent Outbreak of Enterohaemorrhagic Escherichia Coli in Japan

An epidemiological consideration on the recent outbreak of enterohaemorrhagic Escherichia coli(EHEC) infection in Japan.

Japan International Cultural Exchange Foundation

Mitsuhiro Kamaku

[There was no date on this paper. SproutNet]

Abstract

An outbreak of enterohaemorrhagic Escherichia coli infection occurred in Sakai City (Osaka Prefecture) in July 1996. Most of the reported cases are children from elementary schools of the municipality, which seemed to be closely related with the intake of school lunches of particular days. The reported number of EHEC infection in Japan, 1996 reached 10,120 including 12 death cases, and sporadic infections continue in 1997 (948 infections [714 symptomatic cases and 234 asymptomatic carriers, including 2 death cases] as of July 17)1,2 [It is odd that these references to 1997 are both written in 1996, SproutNet].  The responsible foods have not been identified with certainty except for about 40 isolated cases. Continuous epidemiological investigation and observation of food safety are important for the prevention of the food poisoning from E. coli O157 : H7 in Japan.

Introduction

Large outbreaks of Enterohaemorrhagic Escherichia coli O157 : H7 infections have been occurring in Japan since late May 1996. Initial clusters occurred in Hiroshima and Okayama prefectures and the extraordinarily large outbreak affected the city of Sakai, Osaka prefecture in July 1996. The outbreak caused reported 6,561 but actually more than 11,000 cases. The food poisoning from E. coli O157 : H7 has been sporadically occurring this year. E. coli O157 : H7 infections are sometimes considered as a emerging infection in the world. I took the epidemiological consideration of the large scale outbreak in Japan.

Methods

Various reports including the public announcement from the Ministry of Health and Welfare3) and the National Institute of Infectious Diseases are collected and carefully analyzed. As to the raw data of every outbreak, information from local governments and institutes through INTERNET was very helpful2).

Results

Large outbreaks of Enterohaemorrhagic Escherichia coli O157 : H7 infections have been occurring in Japan since late May 1996. Initial clusters occurred in Okayama (497 infections [496 symptomatic and 1 asymptomatic cases, including 2 death case]) and Hiroshima (197 infections [185 symptomatic and 12 asymptomatic cases]) prefectures. And then an extraordinarily large scale outbreak of E. coli O157 : H7 infection occurred in the city of Sakai, Osaka prefecture in July 1996, which caused reported 6,561 cases but actually believed to have affected more than 11,000 people. A total of 6,309 schoolchildren and 92 School staff members were affected and another 160people have contracted secondary infections1),4). Since 8 August, no new cases have been reported in Sakai city. The number of hospitalized patients peaked at 534 on 18 July 1996 and the number of patients suffering from hemolytic uremic syndrome (HUS) peaked at 101 on July 24 1996. Three, a 10-year-old girl (died on 23 July 1996), a 12-yaer-old girl (died on 16 August 1996) and 7-year0old girl (died on 1 February 1997)had died.

The epidemiological investigation revealed that fresh radish sprouts, which are popularly eaten raw in Japan, were the food eaten in common by the school by the schoolchildren as school lunches on particular days. Another outbreak occured also in July 1996 in a home for the elderly in a surrounding city of Osaka prefecture (119 people affected [98 symptomatic and 21 asymptomatic cases]) and three other small outbreak in a workplace in Kyoto city, at a hospital and day nursery in the Osaka metropolitan area. On these outbreaks the radish sprouts produced by the same farm in Osaka prefecture had also been consumed. The DNA patterns of E. coli, analyzed by the National Institute of Infectious Diseases, Japan were identical among the isolates from these five outbreaks. However, samples of radish seeds and water for cultivation from the radish sprout farm concerned, showed no trace of E. coli O157 : H7 1),4).

Sporadic outbreaks of E. coli O157 : H7 continue in 1997 in Japan. From the beginning of the year 556 infections (377 symptomatic cases and 179 asymptomatic carriers, including 1 death case)) were reported as of June 24. The responsible foods have not been identified with certainty except for 43 isolated cases since July 1996. Thirty-one cases (72%) were closely related to the products of cattle, and in the recent two cases fresh radish sprouts were confirmed as responsible food.

Discussion

Judging from the above mentioned evidence, fresh radish sprouts were epidemiologically suspected to be the responsible food of the outbreak of E. coli O157 : H7 infection occurred in Sakai city. The fact that water and soil from the environment of the radish sprout farm concerned will not be a disproof of responsible food, remembering the historically famous outbreak of Cholera in London in 1850s, investigated by Dr. Snow. The responsible food, however, considered to be fresh radish sprout of particular farm and shipped on particular three days (7,8 and 9 August 1996.) Considering the reservoir of the pathogen (mainly cattle) and the economic impact on producers of radish sprouts, more careful attention should have paid on the announcement of responsible food.

In Japan school lunch program is generally introduced at most of elementary and high schools, and collective delivery of various raw and processed food from regional food delivery centers is not unusual, which could be a hotbed of mass outbreak of food poisoning. The preserving condition of food in school kitchens after the daily delivery and the intermingled preservation of different kinds of food seemed to be the supporting factor of the outbreak in Sakai city. School lunch system and collective delivery system should be reconsidered from the preventive point of outbreak of food poisoning.

Enterohaemorrhagic Escherichia coli O157 : H7 infection will continue to be an important health concern especially in developed countries. Continuous epidemiological investigation, improvement of food safety system in every field including the introduction of Hazard Analysis Critical Control Point (HACCP) and observation of rules of food safety are important for the prevention of the food poisoning from E. coli O157 H7 in Japan.

References

  1. Enterohaemorrhagic Escherichia coli infection, Japan. WHO Weekly Epidemiological Record No.30 : 229-230, 1996
  2. National Institute of Health Science Home Page : Topics on the outbreak of E. coli O157 : H7, 1997
  3. Ministry of Health and Welfare : The report on the investigation of the outbreak of diarrhea among school children in Sakai city, September 1996
  4. Food safety-Enterohaemorrhagic Escherichia coli infection, Japan. WHO Weekly Epidemiological Record No.35 : 267-268, 1996

E-mail : mkamakur@po.iijnet.or.jp
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