The Topic of This Month Vol.28 No.5(No.327)

Enterohemorrhagic Escherichia coli infection in Japan as of April 2007

(IASR 28: 131-132; May, 2007)

In compliance with the Law Concerning the Prevention of Infectious Diseases and Medical Care for Patients of Infections (Infectious Diseases Control Law), enterohemorrahagic Escherichia coli (EHEC) infection is classified as a category III notifiable infectious disease under the National Epidemiological Surveillance of Infectious Diseases (NESID) and reporting by physicians is mandatory. The case definition has been amended in April 2006 as follows: In cases of hemolytic uremic syndrome (HUS), notification is also needed if Verocytotoxin (VT) is detected in feces, or O-antigen agglutinating antibody or anti-VT antibody in serum (IASR 27: 149, 2006). When a physician makes notification of food poisoning or the director of a health center recognizes food poisoning, each local municipality conducts investigation and reporting to the national government under the Food Sanitation Law. Prefectural and municipal public health institutes (PHIs) undertake EHEC isolation, serotyping and VT typing and the Department of Bacteriology I, the National Institute of Infectious Diseases (NIID), conducts molecular epidemiological analysis of the isolates and provides information by Pulse-Net Japan (see p. 134 of this issue).

Notified cases under the NESID: In 2006, 3,922 new symptomatic and asymptomatic cases of EHEC infection (hereafter referred to as cases of EHEC infection) were reported (Table 1). The tendency of gradual increase since 2004 is still continuing. As usual, the peak of epidemic was seen in summer (Fig. 1). The incidence per 100,000 population by prefecture was the highest in Miyazaki Prefecture (11.45), followed by Saga (10.62), Toyama (10.35), and Kumamoto (8.25) Prefectures. A considerable regional difference was seen as usual (Fig. 2). In the regions where many cases occurred during 2002-2005, many cases tended to occur also in 2006. Cases that acquired infection in foreign countries markedly increased in 2004 (151 cases), decreased in 2005 (27 cases), and increased again to 54 cases in 2006. A largest number of cases of EHEC infection in 2006 were 0-4 years old, followed by 5-9 years old. Of cases of 0-14 years old, there were more males and of those of 15 years or older, there were more females. The rate of symptomatic cases was high among younger and the aged generations (75% under 19 years old and 79% above 65 years old) and lower than 40% among thirties and forties (Fig. 3).

EHEC isolation: Reports of isolation of EHEC from PHIs to NIID counted at approximately 2,200, which was smaller than cases of EHEC infection (Table 1). This is due to the fact that not all reports of isolation outside of PHI are reached under the present system.

The ratio of O157:H7 was on the gradual decrease, being 52%, that of O26 24% and that of O111 3.3% in 2006 (see p. 133 of this issue & Serotypes of some strains producing VT are untypable with the commercial anti-sera (IASR 25: 141-143, 2004). For identification of EHEC, it is necessary first to confirm VT. The types of VT produced by isolates (or the toxin gene possessed) were VT1 & 2 accounting for 68% among O157 in 2006 as usual (53-68% during 1997-2005), among O26, VT1 alone accounted for 96%, and among O111, VT1 & 2 accounted for 46%.

Of 2,154 cases in which EHEC was detected in 2006, the symptoms of 1,466 cases from which O157 was isolated were bloody diarrhea in 34%, diarrhea in 55%, abdominal pain in 50%, fever in 20%, HUS in 24 cases (VT1 & 2 in 16 cases, VT2 alone in seven cases and VT1 alone in one case). In addition, HUS was reported in four cases of O111 (VT1 & 2 in three cases, and VT1 alone in one case) and in one case of O26 (VT1 alone). Since the report of detection of EHEC positive for VT1 alone from HUS cases used to be rare, it may be possible that VT2 was missed to be detected in the present cases of VT1 alone.

Of 178 cases in which HUS was reported in 2000-2006, those younger than one year were 21 cases (1.9% of 1,135 cases from which EHEC was isolated), 2-5 years 88 cases (3.1% of 2,810 cases), 6-15 years 40 cases (1.7% of 2,370 cases), 16-39 years 9 cases (0.3% of 3,434 cases), and over 40 years 20 cases (0.7% of 2,681 cases). Among younger generations, the number of cases was large and the incidence rate of HUS high.

Outbreaks: Among 28 outbreaks of EHEC infection reported by PHIs to NIID in 2006, 17 were due to O157. In 18 outbreaks involving 10 or more EHEC-positive cases (Table 2), O157 and O26 accounted for half the numbers and the suspected route of infection in five were thought to be due to foodborne transmission and nine due to person-to-person transmission. As cases that acquired infection in foreign countries, an outbreak among participants of a school excursion to China were reported in 2006 (see Table 2 No. 15 & p.142 of this issue) following those in 2003 (to Australia) and 2004 (to Korea).

In 2006, there were 24 incidents of EHEC food poisoning involving 179 cases (provisional data) reported from prefectural governments in compliance with the Food Sanitation Law (note: the number of cases was much smaller than that reported under the Infectious Diseases Control Law, due to the fact that incidents in which food was incriminated as the source of infection were few, and also that incidents involving only a single case are not always reported as food poisoning).

Since EHEC, as is the case with Shigella , causes infection with a minute quantity of the organisms, infection is liable to expand by person-to-person transmission. In 2006, outbreaks in nursery schools and kindergartens remained many (Table 2), therefore it is necessary to take proper precautions, including hand washing by children and staff members and sanitary control of paddling pools for children in summer (see p. 139-142 of this issue). When a case occurs, secondary infections among family members may often follow, therefore thorough instruction to family members is required to prevent secondary infections.

Food contaminated with a minute quantity of the EHEC organisms may cause infection. Since consumption of raw or undercooked meat may often be incriminated, it is important to keep basic precautions against food poisoning such as thorough cooking of food items (see p. 135-139 of this issue).

In 2006, infections presumably caused by experience of touching with cows on a meadow or sheep raised at school were reported (see Table 2 No. 3; IASR 28: 116-118, 2007, IASR 27: 265-266, 2006, IASR 28: 13-14, 2007 and IASR 28: 46-47, 2007). After contact with animals, it is necessary to take care by thorough hand washing (a notice from MHLW on July 4, 2006).

Update 2007: During the 1st through 17th weeks in this year, reports of cases of EHEC infection counted at 236 (Table 1). Increase in EHEC infection toward coming summer is anticipated, so it seems necessary to call further attention.

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