San Francisco Chronicle | June 28, 2008
By Sabin Russell

A widespread practice of mixing tomatoes from different farms at produce distribution centers has made it impossible so far to trace the source of a nationwide salmonella outbreak that has sickened hundreds, federal regulators said Friday.

Dr. David Acheson, an associate commissioner for the Food and Drug Administration, acknowledged that the extent of the practice, known as "repacking," was a surprise to agency investigators, and that it vastly complicates the process of tracing the path of tomatoes from farm to store.

"We are learning that this is a very common practice," said Acheson. "Possibly 90 percent of tomatoes are repacked."

The agency has found, for example, that tomatoes from Mexico have been shipped to Florida, repacked and sold with tomatoes from Florida. Similarly, tomatoes from the United States are sent to Mexico, where they are repacked and shipped to the United States as a product of the United States.

None of these juggled tomatoes has yet been linked to the salmonella outbreak, but the practice illustrates one reason why FDA disease detectives have had no success in tracking the bug back to the farms in Mexico or southern Florida, where they think it may have originated.

"We've got to examine the whole traceability system," Acheson said. 

Meeting customer needs

Distributors frequently repack tomatoes to meet the needs of commercial customers, such as restaurant chains, that demand that each box contain vegetables of similar size and ripeness.

Not only does repacking make it harder to figure out where a bad tomato may have been grown, it raises the prospect that consumers who think they are buying produce from one of the many designated "safe" states - California is one of them - may be getting tomatoes comingled with produce from other regions.

No tomatoes grown in California have been implicated in the outbreak, but fear of the bug has spread chaos in the nation's fresh tomato industry.

Acheson said investigators are inspecting warehouses nationwide to see if the repacking process is a source of contamination, which has been going on since April and has spread to 36 states. He acknowledged that tomatoes from suspect regions may have traveled to repacking sheds that handle tomatoes from areas the FDA had declared safe.

Attempts to find sources of vegetable contamination are notoriously difficult, because the product is perishable, tends to be consumed quickly, and seldom has the kind of labeling found in processed foods. 

"It is possible that this investigation will not provide a smoking gun that allows us to pinpoint a source," said Acheson. "With repacking built into this as a potential problem, it is obviously important for us to re-examine what we are doing here."

Commingling forbidden

Jay Van Rein, a spokesman for the California Department of Food and Agriculture, insists that this is not likely to be a problem for consumers of California tomatoes, because state law forbids co-mingling when the produce is sold with the state name on the label.

"Almost every California grower wants to add 'California' to their label," he said. 

Jim Gorny, executive director of the Postharvest Center at UC Davis - which specializes in the study of produce distribution - said one problem with repacking is a lack of control over what boxes are used when one batch is emptied and another refilled. A box from Florida could easily be refilled with tomatoes from a box from Mexico, and vice versa.

However, he said that because tomato shipments from areas still under suspicion for the salmonella outbreak are being closely monitored, it is unlikely at this point that contaminated tomatoes would reach a repacking plant. "I don't think consumers should be alarmed by this at all," he said.

Disease investigators are puzzled that salmonella cases continue to be recorded long after the harvests have been completed in south Florida and Mexico where the contamination was thought to take place.

"We have no evidence that the outbreak is over," said Dr. Patricia Griffin, an epidemiologist with the Centers for Disease Control and Prevention.

810 reported sickened

At least 810 Americans have been sickened by the strain Salmonella Saintpaul, which can cause stomach cramps, vomiting and diarrhea, making it the largest recorded outbreak of the illness ever traced to produce.

She also acknowledged that, for every reported case of salmonella, there can be as many as 30 people who recover without a visit to the doctor or whose illnesses go unreported.

The ongoing nature of the outbreak has also caused disease investigators to consider that some other food product or process may be responsible for the salmonella poisoning.

Fresh tomatoes grown this spring in South Florida and Jalisco, Coahuila and Sinaloa, Mexico, remain the primary focus of the investigation, although tests of 1,700 samples so far have turned up no trace of the bug.

"The source of contamination has been ongoing at least through early June. And we don't have any evidence that whatever the source is, it's been removed from the market," Griffin said.