Updated Monday, Aug. 4, 2014:
No illnesses have been reported since Blue Lake reopened July 23. In addition, water tests taken after the outbreak did not detect norovirus in the water.
Swimming, boating and other water activities will reopen Wednesday at Blue Lake Regional Park in Fairview, ending an eight-day lake closure to investigate an outbreak of vomiting and diarrhea.
Public health officials believe that contact with lake water now poses minimal risk to visitors after a highly contagious norovirus infected dozens of park visitors the weekend of July 11-13. It is likely that the virus spread among swimmers and bathers who may have swallowed small amounts of contaminated lake water.
“Everything is fitting together with our hypothesis,” said Dr. Jennifer Vines, Multnomah County’s deputy health officer. "Including interviews with park visitors and positive norovirus tests from people who got sick. The information suggests that someone had a fecal accident in the lake and introduced the virus."
One routine water sample collected while the lake was closed showed a high E. coli result but all other tests for E. coli have come back at low levels. E. coli and blue-green algae were ruled out as the cause of the illness early on. The Multnomah County Health Department is monitoring results of samples of lake water for E. coli and will send a sample to the CDC to look for traces of norovirus. Results are expected in about a week.
Dr. Vines said testing the lake water for norovirus as the cause does not tell us anything about the actual risk to swimmers. "Expert advice and common sense suggest that waiting at least a week before reopening should be sufficient from a public health standpoint.”
Throughout the investigation, Blue Lake remained open for other activities, including picnics, sports and a splash pad with a separate water source. The Stumptown Half-Marathon will take place Saturday, July 26, as scheduled. However, an affiliated triathlon at the park was canceled due to uncertainty about the lake.
When the lake reopens on Wednesday, July 23, precautionary signs will ask visitors to report vomiting or diarrhea that starts within one to two days of swimming in the lake. The signs will also remind visitors about important measures to avoid spreading illness: Don’t go in the lake if you’re feeling sick and children under age 5 are not allowed in the lake.
Metro will continue doing everything possible to make sure Blue Lake is a fun and safe destination for visitors, said Justin Patterson, parks and property stewardship program director. In addition, Metro will ramp up its regular water testing by collecting daily samples for the next week.
“We always take the cautious approach when it comes to people’s health,” Patterson said. “But we know that Blue Lake fans will be excited to have the whole park available again.”