Last summer’s norovirus outbreak in Multnomah County, Oregon, appears to be linked to swimming in a natural lake in Blue Lake Regional Park, according to a study from the Centers for Disease Control and Prevention.
Swimming in the lake on July 12-13, 2014, was significantly associated with the 65 probable and five laboratory-confirmed cases of norovirus infection that were reported that same weekend, according to the retrospective cohort study. Among the study’s other findings was that people who swam in the lake were more than twice as likely to become ill, compared with others who visited the park that weekend but did not go swimming.
Diarrhea and vomiting were reported by 10 and 14 of the sickened individuals, respectively. A swimmer’s vomit or fecal incident on July 12 is the most likely cause of the lake’s contamination.
Engaging in strategies for preventing high-risk situations in recreational waters, such as Blue Lake’s biweekly water testing for fecal contamination, evidently do not ensure prevention of contamination, according to Amy Zlot of the Multnomah County Health Department and her colleagues.
Additionally, swimming area officials need to educate the public about healthy swimming practices, the researchers said. Toward that end, the agency has recently published a free downloadable brochure on healthy swimming.
Read the full study in the MMWR (2015 May 15;64:485-90).