Forty-five out of 200 people attending an event at the Hotel Sofitel last week may have contracted the highly communicable norovirus, according to county health officials investigating a "very significant” amount of illness reports following a Redwood City-San Mateo County Chamber of Commerce gathering last week.

"At this point, the general theory is that it is the norovirus,” said Director of Environmental Health Dean Peterson. "It can be passed through food but more often it’s human contact, like placing your hand on something or someone infected then putting it to your face.”

The San Mateo County Health Department began receiving reports of illness Monday morning, days after the Jan. 24 chamber event at the high-end Redwood Shores hotel.

The chamber was holding its annual dinner and awards recognition banquet, according to the group’s Web site.

None of the hotel’s other guests or employees came down ill, said Sofitel spokeswoman Janice Maragakis.

Ironically, she said, General Manager Didier de La Ferrier belongs to the chamber and also came down ill. He thought it was simply the flu until the first calls came in, Maragakis said.

"We’re all trying to figure it out. It’s very bothersome but we’re glad that no one is gravely ill,” Maragakis said.

A specific answer won’t be available for a day or two because lab results require up to 48 hours to process, Peterson said.

Norovirus is a group of viruses that cause stomach flu symptoms such as diarrhea, vomiting and stomach cramps. The illness usually lasts one to two days without any long-term health effects, according to the Center for Disease Control. It spreads through contaminated food or liquids, by touching contaminated surfaces or objects and then placing that hand in one’s mouth, or through direct contact with someone who is infected and showing symptoms. It commonly hits military and cruise ships but outbreaks also occur on land at day-care facilities, hospitals and schools.

Outbreaks at hotels are not unheard of although San Mateo County averages only one every year or two, Peterson said.

The Hotel Sofitel has no prior violations or health complaints on record.

As of Tuesday, the reports numbered 45 out of 200, which is a "very significant attack rate” and shows definitely common circumstances amongst those ill, Peterson said.

Investigators are looking at every aspect, he said, from the menu to the health of employees.

"The epidemiologists aren’t ruling anything out,” he said.

Michelle Durand can be reached by e-mail: michelle@smdailyjournal.com or by phone: (650) 344-5200 ext. 102.