Health officials confirmed Friday that a fast-acting gut bug known as norovirus is responsible for an outbreak of illness that sickened more than 200 people gathered for a cheerleading championship in Washington state last weekend.

Results of state laboratory tests showed that that the nasty group of viruses caused the short-but-severe vomiting and diarrhea that affected some people who participated in and attended the state championship and Salute to Spirit cheerleading, dance and drill team event held in Everett, Wash. Norovirus is typically spread through person-to-person contact.

The outbreak was likely precipitated by people who were ill in public, said Suzanne Pate, spokeswoman for the Snohomish Health District.

"Somebody arrived at the event sick," said Pate, noting that janitorial crews were called to clean up vomit in a restroom and on an adjacent walkway. Those areas were likely exposure sites for the cheer and dance teams, she said.

Some 229 people were sickened and least 33 people sought medical attention for their illnesses, state health officials said late Friday. That number is expected to grow as the investigation continues.

More than 3,000 people attended the event Feb. 4, which included more than 1,000 competitors at the Comcast Arena, a popular venue for large gatherings.

A Comcast Arena spokeswoman said officials had sanitized the premises in accordance with federal health guidelines before a new event scheduled for Friday night. Tests of the arena's water supply showed no problems, Pate said.

"It's probably the best-scrubbed place in the county," she added.

State health officials are conducting an online survey of 2000 event participants and their families to identify a common source of illness. Participants have until Feb. 13 to submit the surveys, and results should be available soon after that.

About 20 million cases of gastrointestinal illness are caused by noroviruses each year, according to the Centers for Disease Control and Prevention. Thorough hand-washing with hot water and soap and immediate sanitizing of contaminated surfaces and clothing is recommended to prevent the spread of the bug. If symptoms last longer than 48 hours, people should seek medical care.

Cheerleading camps or competitions have been the source of previous outbreaks, including a 2002 E. coli O157:H7 outbreak in Eastern Washington.

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