Last week, some 300 staff and students in San Francisco were sickened with norovirus believed to have been transmitted by someone barfing on a door handle.

It now appears a similar mode of transmission sickened 229 cheerleaders and cheeries at a Washington state competition.

JoNel Aleccia of msnbc cites Suzanne Pate, spokeswoman for the Snohomish Health District, as confirming Friday that norovirus was the cause, and the outbreak was likely precipitated by people who were ill in public.

"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.

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.