The investigation is in its early stages, and health department investigators haven't yet been able to find a common source for the 24 cases reported since Friday, said Richard McGarvey, spokesman for the department.
Salmonella is a reportable disease in Pennsylvania. Every case that's diagnosed by a doctor must be reported to the health department within 24 hours. The number of cases reported in Westmoreland, Allegheny, Butler and Beaver counties was changing throughout the day Tuesday.
"Cases continue to come in all day long," McGarvey said.
A fairly common illness, salmonella is rarely fatal. Symptoms -- abdominal pain, headache, nausea, vomiting, fever and diarrhea -- can mimic a viral illness or influenza. The incubation period for the illness is 12 to 72 hours, making it hard to trace the source of the infection.
The state health department is looking for "commonality" among the cases reported in the region in an effort to determine the source of the outbreak, McGarvey said.
But that's complicated by the fact that there are more than 100 different types of salmonella bacteria, he said, adding that he would not speculate about a potential source of the infection.
Health department nurses are contacting all patients reported suffering from the illness, asking where they ate, what they ate, where they went and what they did during the last three days, McGarvey said. The questioning will get more detailed as a clearer picture of the outbreak's scope develops.
The search for a source could take investigators to pet stores, farm markets or restaurants. Lizards and iguanas -- popular as pets -- carry one type of salmonella. Raw foods carry another.
Doctors at area hospitals have noticed an increase in patients suffering from salmonella.
Mercy Jeannette Hospital has seen 10 cases, including two people who were treated on an in-patient basis, said Patti Buhl, director of community relations. She said all the cases were mild.
The hospital typically sees about one or two cases of salmonella a year, Buhl said.
"Ten is out of the ordinary for us," she said.
Westmoreland Regional Hospital, in Greensburg, had two in-patients with positive salmonella cultures and 14 other positive cultures from outpatients during the past week, said Linda Gioia, senior marketing specialist. Those outpatient cultures could have come from the emergency room or physicians' offices, she said.
A spokesman for Latrobe Area Hospital would not disclose whether the facility had treated any patients for salmonella. Dorothy Hufford, manager of community relations, referred calls to the state health department.
Recent salmonella outbreaks have been traced to raw almonds, alfalfa sprouts, unpasteurized milk, ice cream, plum tomatoes, pastries, cantaloupe, salsa and orange juice.
The Centers for Disease Control and Prevention, based in Atlanta, estimates that food-borne illnesses infect 76 million people in the United States each year, causing 325,000 hospitalizations and about 5,200 deaths.
Medical costs for the treatment of salmonella alone are estimated at more than $1 billion annually, according to the CDC.