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

Laboratory and Epidemiology Communications

Cryptosporidium Outbreak in a Sports Center
Hajime Yokoi*, Miyoshi Tsuruta, Toshimitsu Tanaka, Mami Tsutake, Yoko Akiba, Tomoko Kimura,
Yoko Tokita, Toru Akimoto, Yoshio Mitsui, Yoshihiro Ogasawara and Hiroshi Ikegami
Chiba City Institute of Health and Environment, Chiba 261-0001, Japan
Communicated by Takuro Endo
(Accepted September 15, 2005)
In late August of 2005, 151 of the 255 people who participated in an August 20 - 24 swimming training in a hotel in
Nagano Prefecture developed diarrhea and other intestinal
symptoms. They belonged to a sports training club with 20branches, 10 of which had joined the swimming training. The
Food and Environment Division of the Nagano Prefecture
Government started investigation on September 1 by collecting
data from Prefectures potentially involved in this incident.
In Ciba City, 39 participants in one club branch in the City
were investigated. The investigation revealed that 38 of 39
participants (97.4%) developed symptoms, and all of them
had used the swimming pool in the hotel. They developed

symptoms from August 24 to September 1 with an incidence
peak at August 28 (Fig. 1). All had diarrhea. Fever (84.2%)
and abdominal pain (78.9%) were also frequent. Diarrhea waswatery, and its frequency varied from several to twenty times
a day. Other symptoms were vomiting (60.5%), nausea(50.0%), headache (31.6%) and chill (10.5%). Two patientsamong the afflicted consulted Chiba Aoba Hospital. The clinical laboratory of the hospital detected in the patients’ stool
specimens oocysts similar to those of Cryptosporidium. Basedon that information from the hospital, our institute conducted
extensive laboratory tests for detection of Cryptosporidium.
We found oocysts of Cryptosporidium in the stool specimensof 30 of the 31 patients we tested during September 1 - 7.
Oocysts from four stool specimens tested further were all ofthe C. parvum human genotype.
Nagano Prefecture Government announced the possibility*Corresponding author: Mailing address: Chiba City Institute ofHealth and Environment, 1-3-9 Saiwai-cho, Mihama-ku, Chiba
261-0001, Japan. E-mail: hajime-yokoi@city.chiba.jp331Jpn. J. Infect. Dis., 58, 2005
12Fig. 1. Incidence of patients over time.

In the present case, the rapid report from the hospital tothe public authority in Chiba City and the timely transfer of
information from Nagano Prefecture to Chiba City greatly
contributed to identification of the source of the outbreak.
The present incident indicates the importance of clinicallaboratories having the capacity to diagnose parasites, anddemonstrates the persistence of parasitic infections, despite
their recent decrease. In cases like the present one, cliniciansand epidemiologists tend to suspect viral or bacterial infections rather than parasitic infections.
The continued exchange of information and epidemiologicalanalysis from wider geographical perspectives is necessary
to detect the links between apparently isolated outbreaks.

that the outbreak was caused by a contaminated swimming
pool in the hotel on the grounds that the patients were limited
to users of the swimming pool or the gymnastic room of thehotel.

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 Surveillance
Report, vol. 26, 168-169, 2005 in Japanese.

No. of patients reported

10864
20
8/24

8/25

8/26

8/27

8/28

8/29

8/30

8/31

9/1

Day of appearance of symptom(s)332