CONCORD -- A Concord delicatessen shut down because of a norovirus outbreak earlier this week was reopened Thursday morning by the Contra Costa County Environmental Health Department.

The North Park Deli on Nelson Avenue was shut down Tuesday, three days after employees there catered an event and more than 100 people ate the food they prepared, said Marilyn Underwood, the county's Director of Environmental Health. But a thorough cleaning of the restaurant convinced the agency it was ready for reopening.

By lunchtime Thursday, a dozen people were waiting in line and many tables were occupied.

"Being so remotely located, we have an emphasis on our customers, because we feed the same people so often," deli owner Johnny Kim said. "A lot of my loyal customers have been back, and they've been very understanding."

Kim, who has owned North Park Deli for 13 years, was forced to close down his establishment after 10 to 15 people who attended a catered event for a company called BioCare Medical, began to develop norovirus symptoms days later, Underwood said. The deli also contacted the agency, she said.

At least 45 people who attended the event have reported norovirus symptoms, Underwood said. The health agency is trying to interview them all, she said, so they can determined what procedures may or may not have been followed.

Underwood said two employees tested positive for the norovirus on Tuesday and that other employees showed a "lack of hand-washing" when the agency went out Tuesday to investigate but praised Kim for the cleaning he did of the deli in the aftermath. Kim was forced to clean his counters with a heavy bleach solution as well as do a thorough cleansing of utensils, plates and other items.

"There's not a surface in here that hasn't been touched," Kim said. "It's been intense."

Kim said his deli never encountered problems with the health department previously and that the nature of the norovirus is to blame. Norovirus symptoms often don't show up in a person for 36 to 48 hours, Underwood said.

The most common symptoms of the gastrointestinal disease are diarrhea, throwing up, nausea and stomach pain, according to the Centers for Disease Control. Other symptoms can include fever, headache and body aches.

"I don't tell my employees to work through their sickness," Kim said. "If they're sick, they go home."

Kim said his deli does a healthy business, with his six employees cranking out between 200 to 300 sandwiches a day. He also said his deli passed a surprise inspection by the Health Department in October without any problems.

Kim said he was grateful that the outbreak didn't cause his customers to go elsewhere.

"To know that people would choose a local business like us over a chain, it means a lot," he said. I'm more thankful than I can express."

Rick Hurd and Daniel M. Jimenez cover breaking news. Follow Rick at Twitter.com/3rdERH and follow Daniel at Twitter.com/DMJreports.