The Health Department is giving shots to 320 employees of the Cheesecake Factory in Providence and the Texas Roadhouse in Cranston after a busboy who worked at both restaurants was found to be infected with hepatitis A.

The busboy apparently picked up the virus, which affects the liver, on a trip to South America. Health officials are convinced that he did not have an opportunity to pass the infection to patrons. He cleared tables and did not handle food.

But his co-workers could have caught the bug from him, so the Health Department is offering injections of immune globulin to all the workers at both restaurants. The injections infuse antibodies against hepatitis A into the body and prevent illness.

Dr. David R. Gifford, health director, said there was no reason for the public to be concerned or to take any preventive measures. The Health Department announced the action so that people could learn about it before hearing rumors, he said. “We want to make sure people understand why we’re doing this,” he said.

Both restaurants remain open.

Hepatitis A is a viral infection of the liver that causes a few weeks of illness but no long-term harm. Only about 25 cases a year occur in Rhode Island, usually when someone travels out the country to places with poor hygiene, Gifford said. The virus is transmitted when people do not wash their hands well after going to the bathroom, and then spread the germ to others with their hands. Symptoms include jaundice (yellow skin), abdominal pain, loss of appetite, nausea, diarrhea, fever, and fatigue.

The Health Department learned of the busboy’s illness late Wednesday afternoon, when a doctor who treated him reported it. Hepatitis A is a disease that doctors must report. Gifford said the busboy developed symptoms three or four days ago. A person can spread the illness for two weeks before having symptoms. Once exposed to the virus, a person will start experiencing symptoms two weeks to two months after being infected.

The Health Department had some doses of hepatitis A immune globulin on hand, and has ordered more. Gifford said the restaurants have agreed to reimburse the Health Department for the cost of the shots, which are to be administered over the next few days, starting last night.

Local health officials held a conference call yesterday morning with the U.S. Centers for Disease Control and Prevention to confirm their view that there was no need to offer shots to the restaurants’ patrons, Gifford said.

The immune globulin shots carry a low risk of soreness or redness at the site of the infection, or fever and aches. They are effective 85 percent to 95 percent of the time.

ffreyer@projo.com