国立感染症研究所

 

 The Topic of This Month Vol. 33, No. 5 (No. 387)


 Enterohemorrhagic Escherichia coli infection in Japan as of April 2012
(IASR 33: 115-116, May 2012)

Enterohemorrhagic Escherichia coli (EHEC) infection is a category III notifiable infectious disease in the National Epidemiological Surveillance of Infectious Diseases (NESID) under the Infectious Diseases Control Law.  Immediate notification after the diagnosis is mandatory requirements for physicians (http://www.mhlw.go.jp/bunya/kenkou/kekkaku-kansenshou11/01-03-03.html).  When an EHEC infection is notified as food poisoning by physicians or judged as such by the director of the health center, the local government investigates the incident and submits the report to the Ministry of Health, Labour and Welfare (MHLW) in compliance with the Food Sanitation Law.

Prefectural and municipal public health institutes (PHIs) conduct isolation of EHEC, serotyping and VT typing, and report the results to Infectious Disease Surveillance Center (IDSC).  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. 127 of this issue).

In year 2011, there was a large O111 outbreak in Toyama and other prefectures which accompanied hemolytic uremic syndrome (HUS) and encephalopathy (see pp. 118 & 119 of this issue).

Cases notified under NESID: In 2011, total 3,938 EHEC infection cases, 2,660 symptomatic patients and 1,278 asymptomatic carriers, were reported (Table 1).  As in previous years, there was a large incidence peak in summer (Fig. 1).  Incidence (cases per 100,000 population) was highest in Yamagata (26.53), Toyama (17.74) and Shimane (10.67) Prefectures, which all experienced large outbreaks (Fig. 2, left panel and Table 2).  As in previous years, incidence of EHEC was highest among the age group of 0-4 years followed by that of 5-9 years (Fig. 3).  Among prefectures, EHEC incidence (cases/100,000) in population under 4 years of age was highest in Iwate, Yamagata and Shimane Prefectures (Fig. 2, right).  Symptomatic cases were, as in previous years, less frequent among people in their 30's, 40's and 50's and more frequent among younger (below 20 years) and older (above 65 years) groups (Fig. 3).  There were 102 HUS cases (including serodiagnosed cases, see p. 130 of this issue), which corresponded 3.8% of the symptomatic cases (see p. 128 of this issue).  Among 61 EHEC-positive HUS cases, 6 cases were isolation positive for both O157 and O111, 42 cases for O157, 9 cases for O111, two cases for O26, and one case each for O121 and for O145; all cases were positive for VT2 with or without VT1.  Seventeen cases were fatal, among whom 11 had HUS.  The number of deaths reported in 2011 was the highest since the NESID started in 1999.

Reports of EHEC from PHIs: In 2011, PHIs reported to IDSC 2,213 EHEC isolates, far less than the reported number of EHEC infection cases (Table 1).  The discrepancy is due to the situation where only a small proportion of isolates in hospitals or commercial laboratories are sent to PHIs.  The most frequent O-serogroups were O157 (59%), O26 (21%) and O145 (5.7%) (see Table on p. 117).  As for types of VTs, VT1-VT2 double positives were 78% of O157 isolates (53-70% in 1997-2010).  Among O26, 79% were VT1 single positives.  Among O145, 50% were VT1 single positives and 47% VT2 single positives.  Frequency of HUS and encephalopathy among O111 cases was exceptionally high (see Table on p. 117) due to the large outbreak as stated below.

Outbreaks: In 2011, PHIs reported to IDSC 29 EHEC outbreaks, including 15 outbreaks caused by O157.  Among 18 outbreaks involving ten or more EHEC-positive cases (Table 2), 13 outbreaks were suspected to be food/water-borne infections, and five person-to-person transmission.  In 2011, 25 EHEC incidents involving 714 patients (including bacteria-negative cases) were reported by prefectures in compliance with the Food Sanitation Law (27 incidents and 358 patients in 2010) (http://www.mhlw.go.jp/topics/syokuchu/04.html).

In 2011, there was a large EHEC O111 outbreak involving yakiniku chain restaurants due to consumption of yukhoe (Korean dish of raw beef and egg yolk) (see pp. 118 & 119 of this issue).  Among 181 patients, O111 was isolated from 85 patients (median age 20 years), among whom 34 patients developed HUS, 21 patients further developed encephalopathy and five died.  HUS cases were more frequent (16 cases) among adult female above 16 years of age.  O111:H8 (VT2 positive) was isolated from the conserved part of the original meet preparations distributed to the chain restaurants.

Prevention and countermeasures: For prevention of EHEC infections, adherence to the principles of food poisoning prevention and avoidance of consumption of raw or under cooked meet are important (http://www.mhlw.go.jp/topics/syokuchu/index.html).  In response to successive food poisoning incidents due to consumption of raw beef meet, MHLW revised the standard of food meet consumable raw (IASR 32: 168-169, 2011 and see p.132 of this issue), and issued the public notice number 321 in October 2011(http://www.mhlw.go.jp/stf/kinkyu/2r9852000001bbdz.html).  In addition, MHLW has considered additional regulation of beef liver consumable raw.  As EHEC O157 are often found deep inside of the liver, MHLW considered prohibition of raw beef liver consumption and already initiated necessary procedures (notice 0409 number 3 issued by Department of Food Safety, MHLW, on April 9, 2012, http://www.mhlw.go.jp/topics/syokuchu/dl/120409_01.pdf).

Similarly as Shigella, EHEC establishes infection even at minute doses and can spread from person to person rather easily.  In 2011, there were not a few EHEC outbreaks in nursery schools (Table 2).  For preventing outbreaks, appropriate hygienic practice, such as routine hand washing and sanitary use of children's padding pools, should be observed.  The health center should provide the patients' family members with thorough instructions necessary for preventing the secondary infections.

Copyright 1998 National Institute of Infectious Diseases, Japan

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