Investigators still don’t know what caused the summer salmonella outbreak among patrons of Sheetz convenience stores, which resulted in 429 confirmed cases among people in nine states.

The search for the source of contamination had a setback in August, reports the Pittsburgh Post-Gazette, when Hurricane Charley hit Florida, home of farms that likely grew the tainted tomatoes at the heart of the outbreak.

Investigators believe that as many as five different strains of salmonella bacteria contaminated the tomatoes served at Sheetz, said Dr. Amy DuBois, epidemic intelligence service officer with the Centers for Disease Control and Prevention. The bacterial variety virtually eliminates the chance that contamination came from an infected food-handler somewhere along the food distribution chain, DuBois said.

The most common reservoirs for the roughly 2,000 known strains of salmonella are wild and domestic animals, so investigators tend to think the contamination occurred either at the farm or in packing sheds where tomatoes are processed. This is surely cold consolation for the owners of Coronet Foods, the Wheeling, W.Va., company that closed this year after it was revealed that Coronet sliced the tomatoes served at Sheetz.