CDC features rare local norovirus outbreak for safe swimming week

May 18, 2015
A rare norovirus outbreak at Blue Lake Regional Park last summer underscores how important it is for swimmers to take bathroom breaks and stay out of the water if they are ill.

The Multnomah County Health Department’s investigation and response into the outbreak that sickened 70 people is featured in the May 15, 2015 Morbidity and Mortality Weekly Report.

The weekly report, published by the Centers for Disease Control and Prevention, is one of the largest health journals in the nation. It is often first to report major health news including AIDS, the cause of Legionnaires disease; and the 2009 pandemic influenza A (H1N1).

The CDC chose to feature the Health Department’s investigation “Norovirus Outbreak Associated with a Natural Lake Used for Recreation — Oregon, 2014’’ in honor of “Healthy and Safe Swimming Week.”

Norovirus is often called food poisoning or the stomach flu. Outbreaks have been commonly reported on cruise ships and in long-term care facilities.  The study reveals how swimming in water that is not chlorinated can also put the public at risk, but that people can easily protect themselves and their families.

“Blue Lake is a beautiful lake and there are many benefits to being physically active in and around water, but people should know there is a risk and there are ways to stay safe,’’ said Dr. Jennifer Vines, deputy health officer, and one of the investigators.

Children are prime targets of ugly bug

About 15,400 people had visited the popular park that July weekend.

When Blue Lake Park staff received three reports of illness that Monday,July 13, 2015, they proactively closed the lake and called Multnomah County.

A small team of county “disease detectives’’ including communicable disease nurses, epidemiologists and health inspectors found and interviewed nearly 140 people. Their analysis revealed that people who swam or waded in the lake were 2.7 times more likely to develop vomiting or diarrhea than those who visited the park but didn’t go in the water.

They concluded the outbreak began after a swimmer with norovirus vomited or had diarrhea and others swallowed contaminated water. Two thirds of those who became ill were children ages 4 and 10.

The lake remained closed for 10 days to control the spread.

“Children are prime targets for norovirus and other germs that can live in lakes and other places we swim because they’re so much more likely to get the water in their mouths,” said Michael Beach, the CDC's associate director for healthy water, said in a statement. “Keeping germs out of the water in the first place is key to keeping everyone healthy and helping to keep the places we swim open all summer.”

Swimmers can prevent rare norovirus outbreak in water

Norovirus is a relatively rare cause of outbreaks linked to swimming. It was identified as the cause of 12 of the nearly 300 swimming-linked outbreaks reported to CDC between 2005 and 2010, the most recent year for which data are available.

Swimmers can help protect themselves, their families and friends by following a few easy and effective steps: 

  • Keep the pee, poop, sweat, and dirt out of the water
  • Don’t swim if you have diarrhea or have been vomiting
  • Shower before you get in the water
  • Don’t pee or poop in the water
  • Don’t swallow lake or pool water

Every hour—everyone out!

  • Take kids on bathroom breaks
  • Check diapers, and change them in a bathroom or diaper-changing area–to keep germs away from the water.

County investigation draws national attention

The report was written by Amy Zlot, Maayan Simckes, Jennifer Vines, Laura Reynolds, Amy Sullivan, Michael McLuckie of the Multnomah County Health Department;  Magdalena Kendall Scott of  the Oregon Health Authority;  Dan Kromer, of Blue Lake Regional Park, and Vincent R. Hill, Jonathan S. Yoder and Michele C. Hlavsa from the National Center for Emerging and Zoonotic Infectious Diseases, CDC.

The story has drawn coverage in Time, Newsweek and other major media. As Dr. Vines and Amy Zlot met television cameras last week under Vines' poster of “Sherlock Holmes,’’ they said their daily investigations into what makes residents and visitor ill rarely get such attention.

“We’re very proud that the CDC has chosen to feature this work,’’ Zlot said.

To learn more about healthy swimming, visit