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The topic of This Month Vol.36 No.5(No.423)

Enterohemorrhagic Escherichia coli infection as of April 2015

(IASR 36: 73-74, May 2015)

Enterohemorrhagic Escherichia coli (EHEC) infection is a systemic infection of pathogenic E. coli that produces Verotoxin/Shiga toxin (VT/Stx) or possesses the VT encoding genes.  Main symptoms consist of abdominal pain, watery diarrhea, bloody diarrhea and occasional high fever (38ºC) and/or vomiting.  Hemolytic uremic syndrome (HUS), which can be fatal among the elderly and children, is attributed to VT that causes thrombocytopenia, hemolytic anaemia and/or acute renal failure.

EHEC infection is a category III notifiable infectious disease under the Law Concerning the Prevention of Infectious Diseases and Medical Care for Patients of Infections (Infectious Diseases Control Law).  A physician who has made the diagnosis of EHEC infection shall notify all such cases to a health center (HC), who then transmits the information to the National Epidemiological Surveillance of Infectious Diseases (NESID) system (http://www.niid.go.jp/niid/en/iasr-sp/2251-related-articles/related-articles-399/3534-de3991.html).  When an EHEC infection is notified as food poisoning by physicians or judged as such by the director of the HC, 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 of the isolates and typing of VT; the obtained data are sent to NESID (see p. 75 of this issue).  The Department of Bacteriology I of the National Institute of Infectious Diseases (NIID), meanwhile, conducts molecular epidemiological analysis of outbreaks using pulsed-field gel electrophoresis (PFGE) or multiple-locus variable-number tandem-repeat analysis (MLVA) methods and, where necessary, confirmatory tests of the isolates sent from PHIs (see p. 83 of this issue).  The NIID’s analysis results are fed back to PHIs and to local governments through the National Epidemiological Surveillance of Foodborne Disease (NESFD) system.

Cases notified under NESID:  In 2014, a total of 4,153 EHEC cases were reported; 2,839 were symptomatic cases and 1,314 were asymptomatic cases (detected during active surveillance of outbreaks or routine stool specimen screening of food handlers) (Table 1).  Owing to multiple large-scale food poisoning incidents, the number of notified cases in 2014 was highest since 2009.  Weekly number of reported cases in 2014 was largest during summer as usual (Fig. 1).  Reports from Shizuoka, Tokyo, Kanagawa, Saitama, Hokkaido and Osaka prefectures occupied 41% of all nortified cases.  The notification rate (cases per 100,000 population) was highest in Shizuoka prefecture (10.26), which experienced a large-scale food poisoning outbreak, followed by Nagasaki (10.24) and Iwate prefecture (10.19) (Fig. 2).  Notification rates within the 0-4 year old population were high in Nagasaki, Iwate and Kumamoto prefectures, where nursery school outbreaks occurred (Fig. 2).  A large proportion of symptomatic cases were among those <30 years and ≥60 years of age, as in previous years (Fig. 3).

A total of 102 HUS cases (3.6% of symptomatic cases) were reported in 2014, and among them EHEC was isolated from 70 cases: their O-serogroup were O157 (56 isolates), O26 (3 isolates), O121 (3 isolates), O111 (2 isolates), O165 (2 isolates), O115 (1 isolate) and the remaining 3 cases were untypable/unknown (see p. 84 of this issue).  Sixty-one isolates were positive for VT2 alone or VT2&VT1, five were positive for VT1 alone, and the remaining four were unknown for VT-type.  Two fatal cases were reported. Among symptomatic EHEC cases, HUS was highest among those <5 years of age (7.2%).

EHEC isolated by PHIs:  In 2014, PHIs reported 2,289 EHEC isolations, much less than the reported number of EHEC cases (Table 1).  This discrepancy is due to the current situation where not all isolates from clinical or commercial settings are sent to PHIs.  The most frequent O-serogroup was O157 (59%), followed by O26 (22%), O145 (4.1%) and O103 (4.1%) (see p. 75 of this issue).  Those positive for VT1&VT2 genes or their toxin products occupied 76% of all O157 isolates as in previous years.  Among O26, O145 and O103, those positive for VT1 alone occupied 97%, 67%, and 100%, respectively.  Information on clinical signs and symptoms was obtained from 1,244 cases among a total of 1,355 O157 cases; the majority were abdominal pain (62%), diarrhea (62%), bloody diarrhea (47%), and fever (22%).

Outbreaks:  Among EHEC outbreaks reported by PHIs to NESID in 2014, Table 2 shows key outbreaks consisting of 10 or more EHEC positives and notable food poisoning outbreaks.  Fifteen outbreaks were suspected to be transmitted person-to-person in nursery schools (see p. 81 of this issue).

Under the Food Sanitation Law, 25 EHEC food poisoning incidents, comprising 766 cases (cases without isolation included) were reported in 2014 (see p. 76 of this issue).  Notable incidents include: O157 food poisoning outbreak attributed to the consumption of contaminated raw horse meat, which spread to 11 prefectures in late March-April (see p. 76 of this issue); O26 food poisoning due to contaminated processed meat in a restaurant chain in 3 prefectures in May-June (see p. 79 of this issue); O157 food poisoning in a restaurant in Chiba prefecture in July (see p. 77 of this issue); and O157 food poisoning of 510 cases, who consumed contaminated lightly pickled cucumbers sold at food stands during a fireworks display in Shizuoka prefecture in August (see p. 80 of this issue).  In addition to these cases, the Department of Bacteriology I, NIID, which conducts molecular epidemiologic analysis, identified identical PFGE and MLVA patterns among EHEC isolates obtained from several sporadic cases without known epidemiological linkage, indicating the possible presence of unrecognized widespread diffuse EHEC outbreaks (see p. 83 of this issue).

Prevention and measures to be implemented:  In response to food poisonings caused by raw beef, MHLW revised the standards of the beef marketed for raw consumption (MHLW notice No. 321, October 2011).  Further, upon the detection of EHEC O157 in the inner part of marketed cattle liver, MHLW banned marketing of cattle liver for raw consumption (notice No. 404 in July 2012) (IASR 34: 123-124, 2013).  The number of reported O157 cases related to consumption of raw beef or raw cattle liver has been declining since.  However, the total number of EHEC cases has not declined, and for reducing the number of EHEC cases it is important to follow safe food handling practices and avoid consumption of insufficiently cooked meat.

EHEC establishes infection even at a dose as low as ~100 bacteria.  It can easily spread from an infected person to other persons directly or indirectly through foods or food material.  In 2014, as in 2013, there were several EHEC outbreaks in nursery schools (Table 2 & see p. 81 of this issue).  Preventing such outbreaks requires appropriate hygienic practice, such as routine hand washing and sanitary use of children’s pools (see “Infection Control Guidelines for Nurseries” revised in November 2012).  In case a member in a family or a welfare facility is infected by EHEC, the health center should give full instructions to the family or the facility on the preventive measures to be taken for preventing secondary infections.

 

Copyright 1998 National Institute of Infectious Diseases, Japan