But that supplier, Wheeling, W.Va.-based Coronet Foods, said in a statement that it tested all areas, equipment, floors, walls, drains and ceilings but found no evidence of contamination.
However, the company said it still decided to suspend purchasing and processessing Roma tomatoes, which represent 1 percent of its line.
Pennsylvania officials had believed tainted Roma tomatoes or lettuce, or both, were to blame, because those who got sick ate those items and because tests showed they ingested a kind of salmonella that is usually found on fresh produce. The unopened bag of tomatoes that tested positive was taken from a Sheetz store in Greencastle, about 60 miles southwest of Harrisburg, near the Maryland border, officials said.
"This test result brings us one step closer to understanding this outbreak," said Joel Hersh, director of epidemiology at the Pennsylvania Department of Health. "Government agencies can now begin the process of finding out how the tomatoes became infected."
The Food and Drug Administration said at least 57 people in Pennsylvania, Maryland and West Virginia who ate at Sheetz convenience stores were sickened as of last week. As of Monday, however, the number of people sickened in Pennsylvania had climbed to 110, state health spokesman Richard McGarvey said.
Those sickened in Pennsylvania got sandwiches from at least 16 Sheetz stores in the Pittsburgh area and along the Pennsylvania Turnpike, company officials have said.
Salmonellosis, an infection caused by salmonella bacteria that can contaminate food or water, generally causes diarrhea, fever and cramps for up to three days. It is not often fatal. The bacteria are spread through the feces of infected animals and humans.
Sheetz chairman Stephen Sheetz said the tests were "good news" for the Altoona-based company, which pulled all tomatoes and lettuce in its 300-plus stores in six states - Maryland, North Carolina, Ohio, Pennsylvania, Virginia and West Virginia. The stores sanitized their deli areas, switched suppliers and brought in new produce.
Company officials had not tallied how much its efforts to stem the bacteria cost or business the company has lost, Sheetz said. People have been buying less food from Sheetz stores, especially in western Pennsylvania where the outbreak was first reported, he said.
"We never looked at the cost. That is something we will tally at the end of the deal. Our job is to make sure the employees and customers are safe and to do the right thing," Sheetz said.
There is no evidence that Sheetz employees spread the bacteria, health officials said.
State agriculture officials still plan to test about 200 samples of lettuce, tomatoes, cheese and mayonnaise taken from 10 Pennsylvania stores to be sure of the cause, said Kristina Watson, a state agriculture spokeswoman.
Also on Monday, a Pennsylvania couple sued Coronet Foods, claiming they became ill from salmonella after eating sandwiches from Sheetz that had the contaminated tomatoes.
In their lawsuit, filed in Pittsburgh federal court, James and Suzanne Groves claim they became ill after buying sandwiches at a Sheetz store on July 2.
James Groves, 40, of West Sunbury, went to the hospital the following day with flu-like symptoms and tests confirmed he was sickened by salmonella bacteria, according to the lawsuit. His wife suffered from similar symptoms but she didn't test positive for the bacteria.
"I was really ill. I have never been that sick," James Groves told the Pittsburgh Tribune-Review in a story published in Saturday's editions. The couple did not return a phone call for comment to The Associated Press on Monday morning.
Among other things, the lawsuit claims Coronet Foods violated an implied warranty that their produce was safe and was negligent because it allegedly didn't do enough to ensure produce was free of the bacteria.
The lawsuit seeks more than $75,000 in damages.