Brief Report: Gastroenteritis Among Attendees at a Summer Camp --- Wyoming, June--July 2006

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On July 19, 2006, the Environmental Protection Agency (EPA) notified the Wyoming Department of Health (WDH) of an Escherichia coli-positive well-water sample, indicating fecal contamination, that had been submitted from a Wyoming summer youth camp after the camp manager noticed cases of gastroenteritis among campers and staff members. This report describes the subsequent investigation by WDH, the Wyoming Department of Agriculture (WDA), and the Wyoming Department of Environmental Quality (WDEQ), which identified Norovirus and Campylobacter species as the etiologic agents.

WDH staff contacted camp managers on July 19; the following day, WDA, WDEQ, and WDH jointly conducted an on-site investigation of the camp, which was located in a mountainous region of southeastern Wyoming. The preliminary investigation suggested a waterborne mechanism of transmission.

The camp usually operated during May--September only, typically hosting campers for approximately 1 week. In 2006, the facility had opened in May for adult weekend retreats, and a longer adult retreat was held during mid-June. No illnesses were reported at either time. The first campers to experience illness were children who attended camp during the week of June 25--July 1, 2006 (Figure). Onset of illness for the first laboratory-confirmed case of Norovirus was July 1, 2006. Additional groups arrived at the camp during each of the following 3 weeks. The number of weekly camp attendees ranged from 29 to 73. The age range of attendees was 7 to 65 years,* although typical groups were composed of adult staff members and campers who were adolescent boys or girls.

Active case finding and surveillance began after WDH was notified of the E. coli-positive well-water sample. Activities included ascertaining the extent of the outbreak, confirming that the camp was the source of exposure, and interviewing all ill persons among camp attendees. Laboratory testing of fecal samples from symptomatic attendees was conducted to confirm the outbreak etiology. In addition, public-health nursing offices were contacted in the home towns of campers, Health Alert Network (HAN) faxes were sent to health-care providers throughout Wyoming, and both Epi-X and the foodborne disease listserv operated by CDC were used to identify ill campers residing in other states. The camp voluntarily closed on July 19 as recommended by WDH until improvements in the camp's water and septic systems could be implemented.

A case was defined as an illness lasting more than 24 hours that included three or more episodes of diarrhea, vomiting, or both, in a camper or staff member after arriving at or leaving the camp during June 1--July 19, 2006. Lists of camp attendees were obtained from camp managers, and a retrospective cohort study was conducted by administering a telephone questionnaire to 210 of 277 (75.8%) campers and staff members. Median age of both ill persons and those who were not ill was 12 years. A total of 141 (67.1%) cases were identified among the 210 interviewed campers. Diarrhea was reported by 102 (72.3%) persons, vomiting by 92 (65.2%), and stomach cramps by 89 (63.1%).

Stool samples were requested from symptomatic interviewees; 23 were obtained and tested for bacterial and viral pathogens at the Wyoming Public Health Laboratory (WPHL). Fifteen of the 23 (65.2%) stool samples were positive for Norovirus, Campylobacter jejuni, or both. Norovirus genogroup 1 alone was identified by reverse transcription--polymerase chain reaction (RT-PCR) in five samples, and genogroup 2 in four samples; C. jejuni alone was cultured from three samples; and both C. jejuni and Norovirus genogroup 1 were identified in three samples. All six C. jejuni clinical case isolates had indistinguishable DNA pulsed-field gel electrophoresis (PFGE) patterns. Persons more likely to develop gastroenteritis were those who drank camp well water from an outdoor spigot (relative risk [RR] = 1.3, 95% confidence interval [CI] = 1.00--1.66, p=0.048) and those who roomed with an ill roommate (RR = 1.50, CI = 1.13-1.98, p=0.005).

Two wells provided the camp with water, which was not treated before use. The wells were 30--50 feet deep, 25 feet apart, and approximately 120 feet from an underground metal septic tank that had been installed in the 1950s. Although these distances comply with the Wyoming State Engineer's Office guidelines for appropriate distancing of wells and septic systems, the guidelines emphasize that minimum distances are site dependent, should take into account local geology, and must be professionally evaluated before the required septic-tank construction permits are issued. The septic tank was filled to capacity when observed during site visits on July 20 and August 3 and had not been maintained adequately over the years. The system did not have a properly constructed leach field (i.e., soil absorption area), and the ground immediately downhill from the tank was damp with sewage. Food-preparation areas had been inspected by WDA before this outbreak investigation and were in compliance with WDA regulations.

Well-water samples collected on July 20 were positive for E. coli. WDEQ and WDH investigators inspected the camp again on August 3, approximately 2 weeks after the camp's closure. Well-water samples collected from the camp at this time were tested at CDC and were negative for both Campylobacter and Norovirus by culture and PCR. However, the 2-week delay from camp closure to sample collection might have limited the laboratory's ability to isolate the pathogens from the water system because uncontaminated groundwater might have replenished the aquifer. Septic system contents tested positive for Norovirus genogroups 1 and 2. Five fresh fecal samples obtained from cattle kept in the area surrounding the camp also were cultured at WPHL. A C. jejuni isolate was identified in one of the samples; however, the PFGE patterns did not match those obtained from campers.

The investigators determined that although the camp met established EPA criteria defining community water sources and although it had not been subject previously to periodic EPA monitoring, the camp's water system should be regulated as a public water system. WDH and WDEQ advised camp directors to remove the septic tank and have a new system installed in an appropriate location, as determined through a professional site evaluation, to decrease the likelihood of future well-water contamination. Installation of either an ultraviolet or a chlorination disinfection unit also was recommended for additional protection. After system improvements have been completed and certified as compliant with EPA regulations, the camp's water system will be subject to periodic EPA testing guidelines and evaluated for coliforms, turbidity, and nitrate content.

This outbreak of gastroenteritis at a summer camp in Wyoming was caused by Norovirus and C. jejuni, which were simultaneously identified in stool samples from ill campers. The investigation emphasizes that multiple etiologic agents should be considered when waterborne disease is suspected and might be related to sewage or septic contamination. A similar outbreak of gastrointestinal illness involving C. jejuni and Norovirus was associated with sewage-contaminated groundwater in Ohio (1), and a waterborne outbreak of Norovirus was reported at a summer church camp in Norway (2). Other recent outbreaks at U.S. summer camps were caused by person-to-person transmission of Norovirus (3).

Investigators of the outbreak described in this report hypothesized that the large number of camp attendees overburdened the septic system and created a heavy demand for water from the wells, thereby reducing the groundwater level and allowing septic system effluent to contaminate the water that replenished the wells. The shallowness of the wells and their proximity to the septic tank, combined with the camp's location in a mountainous area with fractured rock aquifers and little topsoil, also might have facilitated contamination by allowing septic tank effluent to percolate to the wells through fissures in the underlying rock formations. An ongoing drought in the area likely was an additional contributing factor that permitted changes in groundwater levels, facilitating contamination. Such factors were identified in a similar outbreak in Wyoming (4), suggesting that alternative waste water treatment methods might be necessary where geologic conditions warrant.

Public health officials, health-care providers, and water-quality regulators should be aware of the potential for septic contamination of well water at rural summer camp sites that lack appropriate water and septic systems. In addition, before sending their children to a summer camp, parents should inquire about recent water-quality testing in the camp, particularly if it is located in a rural area where similar systems are more likely to be encountered.

Reported by: C Van Houten, MS; L Baker, MSPH; K Weidenbach, MPH; K Bryan; T Murphy, MD, Wyoming Dept of Health. H Mainzer, DVM, J Sarisky, MPH, V Hill, PhD, C Fitzgerald, PhD, R Luce, DVM, EIS Officer, CDC.

This report is based, in part, on contributions by W Manley, J Walford, and R Harris, Wyoming Public Health Laboratory; D Finkenbinder, Wyoming Dept of Agriculture; and L Harmon, Wyoming Dept of Environmental Quality.

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