The state Department of Health is investigating what appears to be an outbreak of gastrointestinal illness centered in Haleiwa, with symptoms resembling norovirus, also known as Norwalk virus.

Norwalk virus is an infection that causes gastrointestinal illness — nausea, vomiting, diarrhea and abdominal cramps, but without fever, said Michele Nakata, chief of the Disease Investigation Branch.

"We can’t say definitely until we get laboratory confirmation," Nakata said. "There are lots of different kinds of germs that can cause those types of symptoms."

The absence of fever, however, rules out bacteria such as salmonella, she said.

So far, at least 10 people have reported symptoms to the department.

Nakata noted a large bicycle ride was held Sunday in Haleiwa, where food and drinks were served and where large groups of people congregated. The infected persons reported being sick Sunday and Monday.

The Norwalk virus is often associated with a cruise ship outbreak, but it also occurs in schools and nursing homes. Nakata said it is easy to have environmental contamination where people are in close quarters.

If food handlers are stricken with the virus, they can contaminate the food, Nakata said.

Symptoms typically appear 24 to 48 hours after exposure, but there is a range, Nakata said.

Lab results should be available in one to two days, she said.

Nakata said getting people to submit stool samples has been difficult.

The department recommends food handlers and people who take care of children to take off from work three days after diarrhea ends. Others may return when they feel well enough, but they still pose a risk if they aren’t careful about hygiene, she said.

According to an October 2008 article on the Centers for Disease Control and Prevention website, a study showed that a person could be contagious for 13 to 56 days, an average of 28 days after being infected with Norwalk.

Good, frequent hand-washing is the single most important way to prevent getting sick and spreading germs, Nakata said.