December 15, 2006
Friday AM

After a salad bar's worth of investigations into contamination of produce in several outbreaks this fall, officials still aren't sure they know exactly how spinach, tomatoes and maybe lettuce became targets of dangerous pathogens.

Despite some of the most aggressive corporate and public-health responses yet seen, the food source of the latest E. coli outbreak linked to Taco Bell restaurants may never be pinpointed.

Here are some questions and answers about how the probes have unfolded so far.

Q: Why does it seem that illnesses related to produce seem to be more common? E. coli mostly happens in ground beef, doesn't it?

A: The federal Centers for Disease Control and Prevention says undercooked beef is the biggest source of E. coli outbreaks, but that raw, uncooked produce has become nearly as great a concern in recent years.

Better guidelines for the handling and cooking of hamburger after several big outbreaks in the '80s and '90s have cut down, but not eliminated, E. coli in meat. Still, investigators haven't entirely ruled out ground beef as the source in the Taco Bell cases.

Produce is turning up as a source more often because people are eating more fresh produce, and because the food-distribution chain for fresh fruits and veggies has become much less localized.

Q: Why is fresh produce so susceptible to contamination?

A: Lots of things happen from farm to fork that can allow germs that cause food-borne illness to take hold. Open fields may be close to livestock carrying a pathogen; or on some farms, compost that includes cow manure may be used on fields. Washing may be incomplete, or some step in packaging may become unsanitary.

Increasingly, people are turning to pre-mixed or pre-cut veggies, and some experts suspect that some steps in processing large batches of food or keeping them bagged at less-than-ideal temperatures may play a role.

Q: Why hasn't the Food and Drug Administration cracked down harder on produce growing and processing?

A: The FDA has issued considerable guidance and a few warnings to produce firms in recent years, but there are a lot of players involved and many have resisted too much government oversight. Even now, as growers, processors and retailers work to set new safety standards and allay consumer fears, some are balking at having government inspectors watch every move.

At the same time, the agency has relatively few investigators and scientists assigned to produce issues, and increasing the scrutiny would require more funding from Congress, and possibly new legal authority.

Q: In September, the FDA issued safety advisories about consuming fresh spinach and was able to narrow the source down to three counties in California and then to just a few ranches. With the latest outbreak, there's been so much confusion, with Taco Bell saying the cause was green onions last week, then the government pointing to lettuce this week. What's so different?

A: Investigators got lucky in the spinach outbreak. They were able to interview enough victims early on to connect the illness to spinach, and a few households still had bags in the fridge they could sample and trace back down the chain.

In the latest investigation, the link was initially Taco Bell, and there were samples of some foods at restaurants and processors that could be tested. But as it turned out, the lab tests of those samples haven't turned up E. coli that genetically matches what's been making people sick.

Q: So the initial lab tests that found E. coli on green and white onions were wrong?

A: The test that found the bacterium on green onions was a screening test, which is sensitive to several types of bacteria and not just E. coli. The test is designed to rule out foods as a source so investigators can narrow the suspects. More specific testing of the same samples didn't find E. coli. The germ was found on one sample of white onions, but it wasn't the strain that made people sick.

Q: Now the CDC says the "most likely vehicle" for the infections was chopped lettuce. How did they determine that?

A: They talked to people who got sick with E. coli and to the friends and relatives who ate with them but didn't get sick, and compared notes on what they ate. Even though a lot of the same ingredients go into most items at Taco Bell, investigators were able to use statistical analysis to identify lettuce as the most likely product. Cheese and beef are still suspect, too, but usually are pasteurized and cooked in ways that would kill E. coli.

Q: Then, if they know the lettuce came from one distributor, they should be able to find the source?

A: There's a lot of investigating still to be done, but FDA officials say that because the shredded lettuce was processed in bulk and probably came from several farms, it may be hard to pin down the source of the contamination if it was on a farm and not at the processing plant. Further complicating the probe is the fact that the outbreak apparently started in mid-November, about the time that lettuce harvesting ends in Northern California and moves south into the Imperial Valley.

Q: There's now another apparent E. coli outbreak involving lettuce and the Taco John's restaurants in Iowa and Minnesota. Is this connected?

A: Health-department officials in the two states say DNA fingerprinting confirms that the same strain of E. coli is making people in both states ill, but it is not the same strain identified in the Taco Bell outbreak. Preliminary results also point to lettuce as the common food source there, but since the two strains of bacteria are different, it's probably not connected.

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