EVERETT — The disease that sickened more than 200 people who attended a cheerleading competition at Comcast Area last weekend is norovirus, sometimes called cruise ship disease, health officials say.

And they think they’ve tracked down how the disease spread. Teens became ill with a stomach virus while at the event, said Suzanne Pate, a spokeswoman for the Snohomish Health District.

Janitorial crews were called to clean up the floors of a restroom and adjacent concourse prior to Saturday night’s awards ceremony, she said. The event was a competition among cheerleading and dance teams from across the state.

“Those surfaces where there was illness were contaminated,” Pate said. People could have been infected as they walked through the restroom and concourse areas if they didn’t carefully wash their hands, she said.

Lab tests conducted by the state Department of Health confirmed the cause of the outbreak.

Even before those results were announced, disease specialists believed the illnesses were caused by norovirus because of a large number of people who were sickened so quickly and because of the length of time the illness lasted — 24 to 48 hours.

Norovirus is highly contagious and can spread rapidly. It circulates frequently, sickening an estimated 20 million people nationally each year.

People with norovirus are contagious from the moment they begin feeling ill to at least three days and as much as two weeks after recovery, according to the Centers for Disease Control and Prevention.

Most people get better within one to two days. But it can cause dehydration. That can trigger health problems among the very young, the elderly and people with other illnesses.

News of the cause of the illnesses was announced late Friday afternoon by the state Department of Health. Statewide, 229 teens and adults have been sickened and 33 of those who became ill sought medical care for severe vomiting and diarrhea.

In Snohomish County, 46 people have reported being sickened with those symptoms, Pate said. No breakdown was immediately available on the ages of those who reported being ill.

Some 1,000 athletes and 3,000 spectators were at Saturday’s event.

The state health department sent electronic surveys to all the athletes who attended the event, asking if they, their family members or friends had become ill.

The virus had been circulating for several months in the Puget Sound region prior to the outbreak among those attending Saturday’s competition at Comcast Arena.

“We’ve been seeing it for months, but not at really high levels,” said Dr. Yuan-Po Tu, director of walk-in clinics for The Everett Clinic.

Sharon Salyer: 425-339-3486 or salyer@heraldnet.com