Why it takes so long to trace a bad tomato

Published 16 June 2008

Tomatoes do not carry bar codes, so it is difficult to trace the source of the recent tomato-borne salmonella outbreak; tomatoes coming from Mexico and parts of Florida are prime suspects

Food and Drug Administration (FDA) detectives had a hot lead, narrowing down on a grower who just might have supplied salmonella-tainted tomatoes. Then the patient changed her story: She had eaten a round tomato, not a Roma one after all. “We basically had to throw it all out and start over,” says Dr. David Acheson, the agency’s food safety chief. Why is it taking so long to find the source of those bad tomatoes? It largely boils down to the frailty of human memory and the mysteries of the tomato bin.

Unlike many other foods, tomatoes do not come with bar codes that let investigators quickly track their supplier. Consumers seldom even know what part of the world they were grown in. Moreover, it can take two to three weeks between when someone ate a tainted tomato, got sick, got diagnosed, and health authorities complete testing showing it’s the outbreak strain. This is if people bother going to the doctor. Few do. Lauran Neergaard, AP medical writer, writes that a common estimate is that there are forty cases of salmonella for every one reported to the health authorities, warns Caroline Smith DeWaal, food safety director at the Center for Science in the Public Interest. Let us look at the math: 228 officially listed illnesses in 23 states — and it is clear that “this is a very large nationwide outbreak,” she says. Do some more math: The shelf life of tomatoes from the time they are picked is three to four weeks. The earliest known salmonella case was 10 April, and the latest 1 June. So while it is not clear that all the bad tomatoes are off the market, most illnesses struck in May — and no culprit tomatoes have been found sitting in anyone’s refrigerator. Contrast tomatoes to the 2006 outbreak of E. coli in spinach. A supplier began recalls within days of the FDA warning. About two weeks later, the mystery was solved. The helpful difference: The raw spinach came in bags that some patients still had in the refrigerator, bearing UPC codes that led investigators to a supplier and eventually to the exact field that had been contaminated by wild boars.

Three weeks into the salmonella probe — health authorities learned there was an outbreak on 23 May, although tomatoes did not become a suspect until 31 May — authorities have run into a