Jpn. J. Infect. Dis., 58, 2005

Laboratory and Epidemiology Communications

An Outbreak of Shigatoxin-Producing Escherichia coli O157:H7
in a Nursery School in Mie Prefecture
Akira Sugiyama*, Yoshito Iwade, Shigehiro Akachi, Yoko Nakano, Yukari Matsuno,
Takuya Yano, Akinori Yamauchi, Osamu Nakayama, Haruko Sakai1, Ken-ichi Yamamoto2,
Yuji Nagasaka2, Takashi Nakano3, Toshiaki Ihara3 and Hitoshi Kamiya3
1

Mie Prefectural Institute of Public Health and Environmental Sciences, Mie 512-1211,Mie Prefectural Kuwana Health Center, Mie 511-8567, 2Mie Prefectural Yokkaichi Health Center,Mie 510-8511 and 3Mie National Hospital, Mie 514-0125, Japan
Communicated by Haruo Watanabe(Accepted October 31, 2005)
on August 3. Class A, the same class in the nursery schoolthat the patient had attended, included numerous pupils withdiarrhea symptoms. It was also discovered that a hospitalized nursery school pupil presenting diarrhea, bloody stool,and fever since July 27 and negative for STEC O157:H7 onstool investigation had hemolytic uremic syndrome (HUS).
An investigation was then carried out on August 8 by visits
to every house of the nursery school’s employees and theClass A pupils and their families. Isolated instances of pupils
with diarrhea beginning in early July were discovered, andat the time of the survey, more than half of the pupils had
diarrhea. In contrast, 1 - 2 pupils in classes of age 2, 3, 4, and5 years had diarrhea. Different pools were used by each class,and to avoid skin irritation among the infants, a chlorine agent
was added to all pools except the baby pool used by Class A.
Table 1 presents the results for each group investigated.
stx2-carrying STEC O157:H7 was isolated from 13/23(56.6%) pupils 0-1 years old in Class A of the initial patient.
At the same time, investigation among 4 family members of
the initial patient found no symptomatic individuals, and stool
results were negative for all individuals. On August 8-13, stool
investigations were completed for all nursery school pupils,
employees, and families of Class A pupils, and a total of 22
new stx2-carrying STEC O157:H7 infections were discovered, 15 in school pupils, 1 in an employee, and 6 among

A major outbreak of Shigatoxin-producing Escherichia coli(STEC) O157:H7 infection occurred throughout Japan in
1996 (1). Since then, the number of individuals infected
has declined to the 1,000 individuals seen annually (2). STEC
infection often occurs in the form of food poisoning causedby the consumption of bacteria-contaminated food (3,4),
but this infection is also characterized by the occurrence of
secondary infection in which a small number of bacteria
allow establishment of the infection (3,4). In late July 2004,
a 1-year-old nursery school pupil in Inabe, Mie Prefecture,with a mucoid, bloody diarrhea stool demonstrated STEC
O157:H7 infection. Thereafter, other pupils in this pupil’sclass were found to be infected. Additional pupils presenting
similar findings continued to appear in the nursery school,and suspicion arose of institutional infection spreading tofamilies of the pupils. We report a summary of these cases.
An interview investigation was conducted at the school,
and the pupils, employees, and families of the initial classunderwent health examinations and stool examinations. Oneplatinum loop of stool was streaked on a CT-SMAC agar platemedium and inoculated with mEC broth. The material wasthen isolated and cultured on a CT-SMAC agar plate medium(5). Approximately 10 of the gray, semitransparent sorbitol
non-decomposing colonies that proliferated on the medium
were checked for the presence oh the Shigatoxin producing
gene (stx) by PCR (6). Positive colonies underwent biochemical investigation by the IMViC system and were thenserotyped by agglutination reaction with O and H anti-serum(Denka Seiken, Ltd. Co., Tokyo, Japan) (7). Pink, sorbitoldecomposing colonies were also collected in a similar fashion to isolate STEC of serotypes other than O157, and thepresence of stx was investigated by PCR (1,4). Pure, cultured
bacteria were then processed by a BlnI restriction enzyme
for the analysis by pulsed-field gel electrophoresis (PFGE)
with Bio-Rad CHEF-DRII (Bio-Rad Laboratories, Hercules,Calif., USA) (8).
The initial case, No. 1, presented with fever on July 29,
2004, and passed bloody stool beginning on August 1. stx2carrying STEC O157:H7 was detected in the patient’s stoolTable 1. Isolation of Shigatoxin-producing Escherichia coli O157:H7**Corresponding author: Mailing address: Department of Microbiology, Mie Prefectural Institute of Public Health and Environmental Sciences, 3690-1 Sakura-cho, Yokkaichi-shi, Mie 5121211, Japan. Fax: +81-593-29-3004, E-mail: sugiya00@pref.
mie.jpGroup by age(year)

No. ofexamination

No. ofpositive

Positive
percentage

0 - 1 year-old pupil (Class A)
2-year-old pupil
3-year-old pupil
4-year-old pupil
5-year-old pupil

2323273433

13001256.5002.96.1

Class A pupil’s family

7068.6

Family members
except Class A pupil

3900

Staff3013.3

Total of stool examination

279238.2

Preservation foodWiping of the foodpreparation room

2200

1300

*: All isolates were stx2-carrying.

398

family members. In PFGE performed on bacteria isolated
from 23 total individuals, all of the strains demonstrated anindistinguishable pattern. As shown in Table 2, bacteria wereisolated from 6 family members, and all of these individuals
were family of Class A pupils. With the exception of No. 20,patients among family members and nursery care providers
were limited to children age 7 years and under. STEC
O157:H7 was not detected either from stored food of meals
provided between July 21 and July 31 (22 samples) or fromwipes of the food and milk preparation rooms in the school(13 samples).
In this outbreak, epidemiological investigation and laboratory tests for stored food and wipe samples did not indicate
food preparation as the cause, and the source of infection in
the initial case could not be determined. Cases of diarrhea
among the school pupils began in early July, but these were
not investigated, and the source for the infection by STEC
O157:H7 could not be determined. However, in light of thelong latency period involved, and the fact that more than 1month is required from manifestation in the initial patient
until negativity is reached in all cases, there is a strong possibility that some pupils were infected in July, and STEC
O157:H7 was excreted thereafter for a long duration. When

STEC O157:H7 infects infants, the rate of occurrence ishigh, and occasional causation of HUS is not uncommon (9).
However, progress is sometimes asymptomatic, despite
infection. STEC O157 survives for very long durations evenin water and other environments, and even a bacterial quantity of approximately 2 logCFU is reportedly sufficient toestablish infection (3). If infants are diapered, there may be
a delay until diarrhea is discovered, and the child may besent to school despite some amount of diarrhea, which alsosuggests the possibility that infection occurred during a diaper
change, or laterally by way of a pool (fecal-oral). Contamination of the baby pool by bacteria excreted by an infectedindividual and infection of other, healthy individuals using
the pool is also conceivable. Passage of infection to families
may have occurred through underwear soiled with feces orthrough contact within the family. STEC infection is often
discovered in the form of food poisoning in meat or otherfoods contaminated with the bacteria, or in undercooked food,but there are also reported cases of institutional lateral infection, such as we have encountered, in old age facilities (10),child mental health centers (8), child daycare centers (11),and nursery schools (12). When infected individuals are discovered in such settings, efforts to prevent primary infection
through routine management of food preparation are of course
important, as is prevention of secondary infection throughthe spread of or contact with feces of an infected individual.

Table 2. The investigated data of Shigatoxin-producing Escherichia coli
O157:H7 infected patients and carriers
Attribute

Classification

1

pupil

class A1

M

patient

7/8/04

2
3
4
5
6

pupil
pupil
pupil
pupil
pupil

class Aclass Aclass Aclass Aclass A1
1
10
1

FFMFM

patient
patient
patient
patient
patient

9/8/04
9/8/04
9/8/04
9/8/04
9/8/04

7

pupil

5F

patient

10/8/04

8
9

pupil
pupil

14F
M

patient
patient

10/8/04
10/8/04

10
1112

pupil
pupil
pupil

No.6’s elder
sisterclass A
No.8’s elder
brotherclass A
class A
class A

1
1
1

M
M
F

patient
patient
patient

10/8/04
10/8/04
10/8/04

13

familyNo.8’sgrandmother59

Fcarrier

10/8/04

14
15
16

pupil
pupil
pupil

class A
class A
class A

1
1
1F
M
M

patient
patient
patient

11/8/04
11/8/04
11/8/0417

familyNo.12’smother29

Fcarrier

11/8/04

18

pupil

5

M

patient

12/8/04

19

family7Mpatient

12/8/04

20

familyNo.16’s elder
brother
No.16’s elder
brother
No.16’smother31

F

patient

12/8/04

21

family24Mcarrier

12/8/04

22

family37

Mcarrier

12/8/04

23

staff

28

F

carrier

12/8/04

class Apupil’sfatherclass Apupil’sfathernurse

Age Sex

This article appeared in the Infectious Agents Surveillance
Report (IASR), vol. 26, p. 142-144, 2005 in Japanese.

Patient/ Determined
carrier
date*

No.

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