FDA is moving ahead with the tomato search -- called a "trace-back" -- even though public health officials haven't yet determined whether tomatoes, lettuce or some other food product was the vehicle for the salmonella contamination, said Ellen Morrison, director of crisis management at FDA.
State agriculture officials found Monday that one tomato sample from Sheetz was contaminated with salmonella. But it that turned out that it was a different strain of the bacteria than the one blamed in the multistate outbreak, which has sickened roughly 160 people.
"Normally, we wait for a particular food to be implicated in an outbreak before we begin a trace-back," said Morrison. "But we felt as a precaution we should begin a trace-back of the tomatoes."
The number of Pennsylvanians sickened grew by 20 yesterday, to 130 cases, with anywhere from 16 to 50 people with salmonella in other states linked to the outbreak.
Morrison noted there may never be a finding of just how food served at Sheetz became contaminated.
"What people don't necessarily understand is that trace-back is not always going to give you a definite answer," Morrison said.
Investigators looking at salmonella outbreaks linked to tomatoes in 1990 and 1993, for example, found practices in a South Carolina packing shed that might have allowed for contamination. But the precise cause wasn't found, said Dr. Michael Osterholm, a food safety expert at the University of Minnesota.
Sheetz purchased 99 percent of the sliced Roma tomatoes distributed by its supplier, Coronet Foods of Wheeling, W.Va. FDA officials visited Coronet Foods last week, a company official said yesterday, and they are expected again this week, according to a West Virginia public health official.
Morrison said she could not comment on the ongoing investigation. She also said it was too early to say how many farms and distributors handled the tomatoes processed by Coronet Foods.
An official of Coronet Foods said Monday that the form of salmonella found on its tomatoes does not typically cause illness in humans. But an investigator with the U.S. Centers for Disease Control and Prevention disputed that yesterday.
"Just about any strain of salmonella can cause sickness in humans," said Dr. Patricia Griffin, a salmonella expert with CDC.
The 130 cases in Pennsylvania are spread among 31 counties.
Allegheny County officials said yesterday that they have recorded 12 salmonella cases associated with the outbreak. Even so, Dr. Bruce Dixon, director of the Allegheny County Health Department, commented: "The new cases are pretty much over."
People infected with salmonella develop diarrhea, fever and abdominal cramps 12 to 72 hours after infection. The illness usually lasts four to seven days, and most people recover without treatment.
Richard McGarvey, spokesman for the state Department of Health, said all those sickened ate during the first 10 days or so of July. The numbers keep going up because more people are getting tested in response to news media reports about the outbreak, McGarvey said. He said presence of the bacteria can be detected in the stool for a few weeks, even after symptoms have subsided.
Meanwhile, the state Department of Agriculture finished testing 235 food samples taken from Sheetz convenience stores and a few food warehouses that also had products from Coronet Foods. Aside from the salmonella finding on Monday, none of the samples tested positive for contamination, said Bobby McLean, director of the food safety bureau for the agriculture department.
The food products tested were tomatoes, lettuce, mayonnaise and cheese. Health officials believe food was contaminated before arriving at Sheetz. Sheetz and Coronet removed all Roma tomatoes from their establishments once the outbreak was discovered.
Maryland has seen 20 cases of salmonella among people who had contact with Sheetz, although it's not clear if they all ate at the stores. Nonetheless, 12 of them have probable or confirmed cases of the Javiana strain of salmonella.
Ohio has seen 13 cases among patients reporting a food history at Sheetz, including two sickened by the Javiana strain.
West Virginia was reporting 17 salmonella cases yesterday among people who ate at Sheetz in June or July. Two of those were sickened by the Javiana strain.