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

Laboratory and Epidemiology Communications

Secondary Transmission of Cryptosporidiosis Associatedwith Swimming Pool Use
Sadato Ichinohe*, Tokunin Fukushima1, Kazunori Kishida2, Kenichi Sanbe,
Shizuko Saika and Makoto Ogura
Division of Epidemiology, 1Division of Living Environmental Science andDivision of Bacteriology, Chiba Prefectural Institute of Public Health, Chiba 260-8715, Japan

2

Communicated by Takuro Endo
(Accepted November 8, 2005)
ity also alerted and called citizens’ attention to the infection.
N and K public health centers that control the two swimming pools searched for possible secondary infection throughthe use of the two swimming pools. A search was made forpeople developing diarrhea, abdominal pain or fever later
than August 25 from among the population who had a chanceof contracting secondary infection, i.e., those who did notparticipate in the joint training in Nagano Prefecture but usedeither of the two swimming pools. Investigation by N publichealth center identified 41 symptomatic patients among 1,819(2.2%), and investigation by K public health center identified
7 symptomatic patients among 1,004 (0.6%). Cryptosporidium
was detected from one of the four symptomatic patients (firstsymptom on September 10) in N public health center andfrom one of the two symptomatic patients (first symptom onSeptember 9) in K public health center (Fig. 1, Table 1). These
cases were considered as secondary infections on the following grounds. First, the patients used the swimming pools fromwhich Cryptosporidium oocysts were detected. Second, there
was a cluster of patients with diarrhea and other symptoms
in the 1st to 2nd week of September and the oocysts wereCryptosporidiosis is a diarrheal disease initiated by ingestion of Cryptosporidium oocysts. The incubation period is
2 - 10 days, and the chief symptom is watery diarrhea. The
transmission to humans can occur by close association with
infected animals, via person-to-person transmission, or fromcontaminated drinking water or less frequently a sprinkler
fountain or a swimming pool (1,2). Here, we report secondarytransmission of cryptosporidiosis through using a swimming
pool.
From August 20 - 24, 2004, school children in a sports
center participated in a joint swimming training in Nagano
Prefecture using a swimming pool in a hotel. Two hundred
and twenty-two among 273 participant children developed
diarrhea and other intestinal symptoms from August 20 to
September 1 with a peak incidence at August 27. The outbreak was considered to be cryptosporidiosis caused by useof the contaminated swimming pool in the hotel.
After returning from the joint training, the participants used
10 swimming pools belonging to the sports center in Chiba
Prefecture. On September 4 these swimming pools wereinvestigated for the presence of Cryptosporidium oocysts, andon September 8 it was recognized that two of them tested
positive.
The Chiba Prefecture public health authority suspended
use of the two swimming pools and ordered that they becleaned. The family members of patients were advised toconsult doctors when they developed symptoms. The author-Table 1. Results of investigation by N and K public health centers

No. of people investigated
No. of patients with symptoms (%)
No. of patients investigated for stool
specimens
No. of patients positive for the oocysts
No. of oocysts detected (per 20 liter)*Corresponding author: Mailing address: Division of Epidemiology, Chiba Prefectural Institute of Public Health, 662-2 Nitonacho, Chuo-ku, Chiba 260-8715, Japan. Tel: +81-43-266-7996,
Fax: +81-43-265-5544, E-mail: s.ichnh@ma.pref.chiba.jp
400

N public
health center

K public
health center

1,819
41 (2.2)
41,0047 (0.6)
2130

12

14

primary infections
secondary infections

Number of Patients reported

1210

8

6

4

2

15-Sep13-Sep11-Sep

9-Sep

7-Sep

5-Sep

3-Sep

1-Sep

30-Aug28-Aug26-Aug24-Aug22-Aug20-Aug0Date of apperance of symptoms
Fig. 1. Incidence of patients in the primary infection (infection at a hotel in Nagano Prefecture) and in the secondary infection(infection at swimming pools of the sports center in Chiba City).

detected from two of six patients examined. Third, the incubation period of cryptosporidiosis is 2 - 10 days (average 7 days),and the oocysts continue to be released for 2 - 4 weeks evenafter symptoms subside. Fourth, the oocysts are strongly
resistant to the chlorine concentrations routinely used fordisinfection of the swimming pools. Because infected patients
continue to release oocysts in their stools for a long timeafter the disappearance of symptoms, it is recommended thatpatients be prohibited from using swimming pools for at least
for 2 weeks after the disappearance of their symptoms (3).
This is an important guideline in preventing the spread ofcryptosporidiosis.

Report (IASR), vol. 26, p. 169-170, 2005 in Japanese.
REFERENCES
1. Centers for Disease Control and Prevention (2004):
Cryptosporidium infection. p. 1-4. Revised. CDC Fact
Sheet for the General Public.
2. National Institute of Infectious Diseases and Tuberculosis and Infectious Diseases Control Division, Ministryof Health, Labour and Welfare (2005): Cryptosporidiosis,
as of June 2005. Infect. Agents Surveillance Rep., 26,165’-166’.
3. Committee on Infectious Disease American Academy ofPediatrics (2003): RED-BOOK: Report of the Committee on Infectious Diseases. p. 255-257. 26th ed. American
Academy of Pediatrics, Elk Grove Village, IL.

We thank Prof. Yoshikura, Emeritus Researcher of theNational Institute of Infectious Diseases, for advice on preparing the manuscript.
This article appeared in the Infectious Agents Surveillance401