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Norwalk-Like Virus Outbreaks at Two Summer Camps ---Wisconsin, June 2001

On June 27 and 28, 2001, the Wisconsin Division of Public Health was notified by two local health departments of outbreaks of gastroenteritis* at two summer recreational camps (camps A and B) in northern Wisconsin. This report summarizes the investigation of these outbreaks, which documents person-to-person transmission of "Norwalk-like virus" (NLV) and underscores the importance of cleaning environmental surfaces and the availability and use of hand-washing facilities at recreational camps.

Camp A opened for the 2001 season with a week of staff training on June 10. During this week, several counselors became ill with fatigue, nausea, vomiting, and diarrhea with illness duration of 24--48 hours. Campers first arrived for a 6-day camp session on June 17 and, within 30 hours of arrival, began having signs and symptoms identical to those experienced by the counselors. A second group of campers replaced the previous campers on June 24. Because many persons became ill in the second group, the camp session was canceled, the campers were sent home, and the local public health department was notified on June 27. During the 3-week period, approximately 80 (20%) of 400 campers and camp staff were ill.

The first case of illness was noted at camp B on June 24 when a child arrived at camp with diarrhea. On June 25, another camper became ill with nausea, vomiting, and diarrhea. During the next 5 days, at least 40 (17%) of the 240 campers and camp staff became ill with identical signs and symptoms lasting 24--48 hours. The campers remained at camp B for the full 1-week session.

Inspection of the camps revealed no substantial problems with food storage or preparation; no leftover foods were available for testing. The campers served themselves family style in a single dining hall at each camp. Ill campers were housed in cabins (camp A) or tents (camp B) with campers who were not ill. Most toilet facilities were pit toilets with hand-washing facilities consisting of cool running water. The camps provided no soap or towels at the pit toilets. Nonmunicipal wells were the source of drinking water at the camps. An environmental survey found no deficiencies with these wells.

Stool specimens were obtained from ill campers and staff at camps A and B. Bacterial enteric pathogen testing was negative and reverse transcriptase polymerase chain reaction for NLV was positive for three of the eight specimens from camp A and two of the four specimens from camp B. Samples of the well water obtained 3 weeks after the outbreaks were negative for fecal coliforms.

The camps, which serve boys aged 10--18 years and are affiliated with the same national youth organization, are located 80 miles apart. They shared no food or personnel and no epidemiologic links were apparent between the camps. Gene sequencing to determine relatedness of the viruses is pending. Although the initial sources of NLV were not discovered, the nature of both outbreaks, particularly the onsets of illness during a several day period and the continuation of the outbreak among separate groups of campers at camp A, indicated the infections were spread within each camp by person-to-person transmission.

NLV can be spread from person-to-person by direct contact, fomites, and aerosols (1--3). The close contact of ill and well campers and the rustic setting of the camps probably contributed to person-to-person transmission by contaminated surfaces in the toilet, dining hall, and living facilities. During June 30--July 1, the washable surfaces at the camps were cleaned with a 10% bleach solution and soap dispensers were added to the hand-washing facilities at camp A. No further cases of gastrointestinal illness were reported at the camps after June 30.

Reported by: L Conlon, Oneida County Health Dept, Rhinelander; K Pranica, L Donart, Oconto County Public Health Div, Oconto; M Proctor, PhD, M Simone, L Lucht, T Boers, JP Davis, MD, Wisconsin Dept of Health and Family Svcs. Div of Applied Public Health Training, Epidemiology Program Office; and an EIS Officer, CDC.


  1. CDC. Norwalk-like viruses: public health consequences and outbreak management. MMWR 2001;50(no. RR-9).
  2. Hedberg CW, Osterholm MT. Outbreaks of foodborne and waterborne viral gastroenteritis. Clin Microbiol Rev 1993;6:199--210.
  3. Becker KM, Moe CL, Southwick KL, MacCormack JN. Transmission of Norwalk virus during a football game. N Engl J Med 2000;343:1223--7.

*Defined as nausea, vomiting, or diarrhea in a camper or staff member while at camp A or B during June 10--30, 2001.

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