The salmonella outbreak from fresh tomatoes has sickened hundreds so far — with many more sicknesses presumably going unreported — in 36 states, and the FDA has still not identified the source of the pathogen. Sabin Russell, the San Francisco Chronicle's medical reporter, yesterday revealed that a major reason for the investigation's stagnation is that tomatoes from many regions are mixed together as they move through the stages of commerce. The practice is known as "repacking": tomatoes are shipped from Mexico to Florida, where they are repacked and sold alongside that state's tomatoes; or a shipment of U.S. tomatoes to Mexico is repacked and trucked back across the border as a product of the United States. Repacking is often done to create cases of tomatoes that have a similar level of red coloration (note that I specifically avoided the word "ripeness" here, because most out of season tomatoes are picked green — and rock hard — then made to turn red by exposure to ethylene gas when purchased by a buyer).
So even if the FDA can figure out which case of tomatoes caused someone to get sick, the label on the suspect case might not correspond to the actual place where the salmonella-tainted tomatoes were grown.
The practice of repacking also has implications for consumers and restaurants. A batch of tomatoes that is supposedly from a salmonella-free state or country could have passed through a repacking house, acquiring some tomatoes from the salmonella region(s) during the repacking.
Tomatoes from California are currently on FDA's "safe" list. They are also less likely to be contaminated by tomatoes from other states because California law forbids packing non-California produce into boxes labeled as coming from California.
All of this is another reason to try to get as close as possible to the source of your food. I do this by buying much of my produce at the farmers market, where I am confident that the items I buy were grown by the people selling them to me, and were only packed once — often just a few hours after being picked.
Photo of tomatoes at the San Francisco Ferry Plaza farmers market by Rachel Cole.