Prince George's County health officials, who closed an Oxon Hill restaurant Monday night after dozens of its customers became ill with salmonella poisoning, began investigating a second unrelated food poisoning outbreak yesterday.

In the latest case, health officials are trying to contact 120 persons who ate at the Forestville Volunteer Fire Department on Saturday and Sunday. Four of those persons have been hospitalized, said Dr. Helen B. McAllister, the county health officer.

The county health department was contacted Monday morning by officials from the fire station, who provided the county health department with a list of people who had eaten at the firehouse over the weekend.

In the earlier case, 13 people who ate at the Ranch House Restaurant at 6355 Oxon Hill Rd. have been hospitalized, McAllister said, including some who became seriously ill.

Health officials initially were in touch with 31 of the restaurant's patrons, but since the salmonella outbreak was reported in the news media Monday night, 199 other customers have contacted the health department. In all of the confirmed cases of salmonella poisoning, she said, the patrons had eaten at the Ranch House on May 30 or May 31.

Officials have been unable to determine the source of either outbreak of food poisoning.

At least 40 foods are possible sources at the restaurant, which will be closed until health investigators find the source of the salmonella outbreak, McAllister said. "In some cases that can take a couple of days," she said. "Probably in this case, it will take a couple of weeks."

The disease can be dangerous, and sometimes fatal, to children, the elderly, or people with weak immune systems.

The types of foods that can carry salmonella include dairy products and chicken, McAllister said. Undercooking food or not storing food in cold enough temperatures can allow the bacteria to multiply, she said. Symptoms of food poisoning include diarrhea, cramps, fever, headaches and vomiting.