SANTA CRUZ — more than two dozen UC Santa Cruz students received an unwelcome visitor during the first week of classes — the stomach flu.

A total of 26 cases of gastroenteritis, commonly called stomach flu, have been reported on campus, and 22 of them came from students living in College 9 or College 10, which are adjacent and share a dining hall.

UCSC has an enrollment of approximately 16,000.

The cause is not known, and the UCSC Health Services is working with Santa Cruz County Health Services on identifying any possible cause.

“We noticed last Friday a cluster of students with acute gastroenteritis,” UCSC Student Health Center Executive Director Mary Knudtson said. “We contacted the rest of campus and contacted the public health department. whenever we see a cluster we work with the health department to identify if it’s a specific virus or bacteria. When we spoke with them, they said the stomach flu was going around the county and not isolated to UCSC.”

An official from County Health Services could not be reached Wednesday to confirm test results on samples from the infected students.

Knudtson said the illness comes on quickly and symptoms, including nausea, vomiting, diarrhea and stomach cramps, typically last for one to two days. It is suspected that the culprit is a norovirus, a common cause of stomach flu that is found in feces and vomit, and is spread from person to person through contaminated food, water and surfaces.

“You tend to see stuff like this in residential areas, nursing homes, college dorms and other clustered populations. It’s also common on cruise ships.” Knudtson said.

In December 2010, an outbreak of norovirus hit the campus of Point Loma Nazarene University in San Diego, infecting about 200 students. in 2008, more than 100 people aboard a cruise down the coast of Baja California were infected with the virus.

The Centers for Disease Control and Prevention offers the following tips for halting the spread of norovirus:

Wash your hands carefully and frequently with soap and water or use hand sanitizer.

take care in the kitchen. Carefully wash fruits and vegetables and do not prepare food while infected.

Clean and disinfect contaminated surfaces.

Wash laundry thoroughly.