Marilyn Underwood, environmental health department director, said the North Park Deli on Nelson Avenue was shut down late Tuesday afternoon. It's uncertain when the eatery will re-open.
Underwood said two employees at the deli have tested positive for the virus.
She said her department was first notified of the illness when 15 people who were at an event catered by North Park Deli on Friday evening became sick over the weekend.
It usually takes 36 to 48 hours after exposure for norovirus symptoms to appear.
Underwood said anyone who visited the deli late last week or early this week and becomes sick should avoid contact with other people. In addition, surfaces and other contaminated items should be cleaned with bleach.
Norovirus is a highly contagious cause of gastrointestinal illness, according to Contra Costa Health Services. It most often circulates in the winter. Sometimes called the "stomach flu," it is not related to influenza. Frequent hand washing is the best way to prevent the spread of norovirus.
Last June, California Pizza Kitchen in Walnut Creek was closed for two days after a norovirus outbreak.
