CDC Alert: Lakes Harbor Norovirus

Cruise ships are not the only place where vacationers can get the dreaded norovirus. A US Centers for Disease Control and Prevention report released today documents an outbreak in a recreational lake in Oregon and warns that swimming in any natural lake can be hazardous.

Dozens of people who visited Blue Lake Regional Park and swam in the lake on a hot July weekend in 2014 were confirmed as having norovirus, with 65 probable and five laboratory-confirmed cases, the CDC said. Officials closed the lake for several days.

“This investigation underscores the need for guidance for determining when to reopen untreated water venues such as lakes associated with outbreaks,” and also shows that health officials need to better inform the public about the risks lake-swimming can pose, the CDC said in the current issue of Morbidity and Mortality Weekly Report.

Norovirus outbreaks are more common in the winter, and CDC data show it causes about 20 million US cases of acute gastroenteritis annually.

The Blue Lake outbreak in Multnomah County, OR, happened in a natural lake, 25 feet deep at its deepest, but one that has a bathing area and beach where the water is shallow.

“A swimmer’s vomit or fecal incident in the lake over the weekend could explain the point source outbreak pattern,” Amy Zlot, MPH of the Multnomah County health department and colleagues wrote.

Since there is no way to chemically treat the lake, the best officials said they could do in a future outbreak is to post signs urging people not to swim if they are ill, not to urinate or defecate in the water, to avoid getting water up their nose, and not to swallow the water. Officials also continue to monitor water quality for bacterial contamination.

The Oregon public health officials had earlier instituted a ban on children under 5 swimming in the lake, but in its report the CDC said it did not recommend that.

The virus is a formidable foe, the CDC reported in the Blue Lake analysis. “There is evidence that norovirus can survive in water for several months and possibly for years,” the authors noted.

Norovirus infection was also confirmed last year in an even bigger incident in Kitsap County, Washington, one that sickened 260 swimmers.

The hunt for a norovirus vaccine is ongoing. Finding one is a goal of the Bill and Melinda Gates Foundation and of several pharmaceutical companies, notably Takeda Pharmaceuticals (formerly Ligocyte).

In March, in an article in PLoS University of North Carolia at Chapel Hill researchers reported promising results with a technique focused on using virus-like particles constructed from molecules of the norovirus’s outer shell. A vaccine made from these particles has elicited an immune response, they wrote.