Norovirus Outbreak in Reno Area Schools Sickens Over 700 Students, Faculty Norovirus is a common virus that affects the gastrointestinal system.

 -- More than 700 students and faculty in the Reno, Nevada, area were sickened after a norovirus outbreak spread to more than a dozen different schools, officials said.

There were 776 cases of norovirus in Washoe County as of Friday afternoon, Phil Ulibarri, public information officer for the Washoe County Health District, told ABC News today.

Those affected include students and faculty at Washoe County School District schools and some day care centers, Ulibarri said.

At one point people were sick with the virus in 17 schools, three day cares and one charter school, Ulibarri said, adding that the number of affected school district schools has now gone down to 15.

One school will be closed Monday, Ulibarri said.

Norovirus is a common virus that affects the gastrointestinal system and can spread widely. Every year the virus leads to between 19 million and 21 million illnesses and 570 to 800 deaths, according to the Centers for Disease Control and Prevention.

Norovirus spreads from an infected person or contaminated food, water or surfaces, the CDC said. The virus causes the stomach or intestines or both to get inflamed, which can lead to vomiting, diarrhea, stomach pain and nausea.

ABC News' Chief Health and Medical Editor Dr. Richard Besser said the virus is highly contagious and can spread from school to school because siblings can share across schools and children from different schools interact outside of school.

Ulibarri also mentioned siblings and outside-school contact as possible reasons for the significant outbreak, and added that the virus may have also spread via school buses. Ulibarri said health officials will be meeting with the school district this week to review protocol.

"We hope that we can get the message across to people that they need to practice good hygiene," Ulibarri said, urging people affected to "wash their hands frequently" and "exclude themselves from school, work and social activities for at least 72 hours after symptoms have subsided."