BACKGROUND: In August 2016, the Kent County Health Department investigated an outbreak of cryptosporidiosis in which all symptomatic individuals (33 students and 7 adults) were associated with the varsity football team at a local high school.
METHODS: Environmental health and epidemiologic investigations were conducted to determine the source of the illness. Preliminary investigation identified a pre-season riverside camping retreat that players, coaches and parents attended prior to onset of illness. Once details of the retreat were obtained, a case control study was conducted to identify exposures associated with illness by calculating attack rates, odds ratios and confidence intervals. A case was defined as gastrointestinal illness occurring within 12 days of the retreat. Confirmed cases had a positive stool test for Cryptosporidium. Controls attended the retreat but reported no illness. Due to the large number of attendees and the difficulty of reaching them by phone, an on-line questionnaire was distributed via e-mail by the school superintendent to varsity football players and coaches.
RESULTS: Eighty-one online questionnaires were completed. The attack rate for primary cases was 49.4% (40/81). In addition to the 40 cases among retreat attendees, 7 cases occurred by secondary transmission among household members and team assistants. A statistical analysis of 28 water exposure variables and 32 food exposure variables determined that participating in a team mud fight was strongly associated with illness (OR=10.82, CI 3.5-33.6 p=.00003). Swimming in the river was also associated with illness (OR=4.39 CI 1.5-12.5, p=.008). A total of seven stool samples tested positive for the parasite Cryptosporidium.
CONCLUSIONS: Cryptosporidium is commonly found in river water and is introduced by human or animal sources. In the days leading up to the retreat, there were heavy rains in the area, which potentially introduced the parasite into the river from surrounding fields. Proper hygiene materials were not available at the rustic campsite and after the mud fight, most players simply rinsed themselves in the river prior to eating dinner. During this investigation, timely physician, school, and electronic surveillance reporting led to early identification of the parasite. Disease prevention interventions, including the cancellation of the team’s first game, prevented further transmission. This outbreak was cited by the district superintendent as “an excellent example of a county health department and a public school district working together in the interests of students and families.” This outbreak serves as a reminder about the pathogenic danger of exposure to river water.