MARTINEZ (KCBS) – Winter is the season when the diarrhea, vomiting and stomach cramps associated with Norovirus start making the rounds at schools and assisted living facilities, and on board cruise ships. Public health officials said this year has been no exception.

In the last two months, nearly 30 schools in Contra Costa County have seen outbreaks of the stomach virus this winter.

READ MORE: Young Graduate Beginning His Career Killed by Falling Tree in Burlingame

That’s not such an alarming number to Erika Jensen, the director of communicable diseases at the Contra Costa County Department of Public Health, although she concedes, “this seems to be a little bit higher than usual.”

KCBS’ Ted Goldberg Reports:

Gastrointestinal illnesses affect one in 15 people across the country every year. For most, the uncomfortable symptoms disappear after a few days. In rare cases, Norovirus can be deadly for the very young and the very old.

If the number of cases at Bay Area schools seems higher this year, it may be because there were fewer cases last year, said Dr. Sara Cody, a deputy health officer for Santa Clara County.

READ MORE: Suspect Arrested In Fatal San Mateo RV Storage Lot Shooting

“This is probably about an average year. It’s quite a bit more than last year, but nowhere near our peak years,” she said.

Although the state of California does not track Norovirus cases, federal statistics show most outbreaks happen between December and April. And this year is showing the same pattern, said Aron Hall, an epidemiologist at the Centers for Disease Control and Prevention.

“We’ve seen relatively average seasons, although when you’re in the midst of the season it can seem overwhelming with the number of outbreaks,” he said.

Hall and the others all emphasized the best way to prevent Norovirus from spreading is hand washing. Otherwise, it’s a few days of bed rest until everything clears.

MORE NEWS: Santa Clara Officials Open COVID-19 Vaccination Clinic At Local Farm

(Copyright 2012 by CBS San Francisco. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed.)