Salmonella bacteria can grow on tomato skin surfaces and infiltrate core tissues during tomato harvest, packing, and transportation. Dicing and pooling of contaminated tomatoes may play a role in further amplifying the amount of contaminated product. Contamination of internal tissue from the outer skin and stem scar can also occur during cutting and slicing. Finally, many Salmonella strains grow rapidly in cut tomatoes held at room temperature, enhancing the risk if tomatoes are maintained at room temperature for extended periods.

Salmonella outbreaks have previously been associated with raw tomatoes, which accordingly should have been recognized as a potential source of contamination. In 1990, a reported 174 Salmonella javiana illnesses, as part of a four state outbreak, were linked to raw tomatoes. In 1993, 84 reported cases of Salmonella Montevideo were part of a three state outbreak that was linked to raw tomatoes.

More recently, in January 1999, Salmonella Baildon was recovered from 86 infected persons in eight states. Raw restaurant-prepared tomatoes were implicated in multiple case-controlled studies. Many restaurants across several states were involved, suggesting the tomatoes were likely contaminated early on, at the farm or during packing, and before distribution.

In July 2002, an outbreak of Salmonella javiana occurred associated with attendance at the 2002 U.S. Transplant Games held in Orlando, Florida during late June of that year. Ultimately, the outbreak investigation identified 141 ill persons in 32 states who attended the games. The epidemiological investigation implicated fresh, pre-packaged, and diced Roma tomatoes as the probable vehicle for the outbreak.

During August and September 2002, a Salmonella Newport outbreak affected the East Coast. Ultimately, over 404 confirmed cases were identified, in over 22 states. Epidemiological analysis indicated that tomatoes were the most likely vehicle, and were traced back to the same tomato packing facility in the mid-Atlantic region. Inspections of that packing facility revealed numerous violations of the Good Agricultural Practices and Good Manufacturing Practices published by the FDA.

In early July 2004, as many as 564 confirmed cases of salmonellosis associated with consumption of contaminated tomatoes purchased at Sheetz Convenience Store were reported in five states, Pennsylvania, Maryland, Ohio, West Virginia, and Virginia. Seventy percent were associated with tomatoes in food prepared at Sheetz convenience stores. Dates of exposure ranged from July 2 to July 16. Five separate serotypes of Salmonella were eventually associated with the outbreak. Most of the cases were infected with Salmonella javiana; other outbreak associated strains were Salmonella typhimurium, Salmonella anatum, Salmonella Thompson, and Salmonella Munched.

FDA investigators traced the contaminated tomatoes back to farms in Florida and possibly South Carolina, but the investigators were also told that farms from five different states may have supplied tomatoes to Coronet Foods at relevant times. The FDA will continue its investigation in early 2005 to observe farm conditions during spring planting.