Bill Marler of the Seattle law firm Marler Clark - which specializes in cases involving food-borne illness - said he will file suit Monday on behalf of six people sickened in the outbreak, including a couple from Butler.
While he indicated that Sheetz is legally liable for tainted food sold at its convenience stores, he is more inclined to sue the supplier who provided the food.
About 44 samples of lettuce, tomatoes, cheese and mayonnaise taken from 10 Sheetz convenience stores across the state showed no trace of the salmonella bacteria, a state Department of Agriculture spokesman said. Testing of an additional 197 food samples will resume over the weekend.
State health department spokesman Richard McGarvey said it could be weeks before officials are able to pinpoint the origin of the outbreak, which has been traced to deli sandwiches garnished with lettuce and tomatoes made between July 2 and Tuesday afternoon, when Sheetz pulled produce from its shelves.
McGarvey likened the hunt to the hepatitis A outbreak at Chi-Chi's Mexican restaurant in Center Township that sickened more than 660 people and killed four.
"We knew it was Chi-Chi's, but it took 2½ weeks to find the particular food item," he said.
The U.S. Food and Drug Administration said Friday it had counted 57 people in Pennsylvania, Maryland and West Virginia who ate food from Sheetz stores and were sickened - but that was before Pennsylvania health officials updated the number of cases in the state to 70.
Dozens more people are sick in Ohio, Virginia and Maryland, but health officials haven't yet determined whether those people also ate food from a Sheetz. The FDA didn't immediately return calls for updated interstate information.
McGarvey reiterated that there is no evidence that Sheetz employees spread the bacteria, and the multiple locations indicate a tainted food supply was the most likely culprit.
Those sickened ate food from 16 Sheetz stores across the state, although he said the bulk have come from the Westmoreland County area. The Sheetz chain is based in Altoona.
McGarvey said a breakdown of salmonella cases by county was unavailable, and officials at The Medical Center, Beaver, Sewickley Valley Hospital and Aliquippa Community Hospital said emergency rooms have been void of salmonella sufferers.
Centers for Disease Control spokeswoman Christine Pearson said two epidemiologists and one medical resident arrived Thursday to help the state departments of health and agriculture trace the specific food item carrying the bacteria.
The FDA and CDC wait for specific food samples to test positive before they review shipping manifests and other records that show where that food originated. From there, federal officials will interview others along the supply chain to determine how the food was contaminated.
State health officials have said they think people were sickened by lettuce or tomatoes because tests indicate that those individuals ingested a strain of salmonella that is usually found on fresh produce.
Travis Sheetz, vice president of operations at the convenience store chain, said all potentially tainted produce was thrown out and the deli areas sanitized. The chain also changed its produce supplier from Coronet Foods in Wheeling, W.Va., he said.
The Associated Press contributed to this story.