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Your Salad: A Search For Where The Wild Things Were

When you tear open a bag of prewashed salad greens, do you worry that this superhealthful fast food could actually make you sick?

The companies that sold you that salad do worry about it. Because no matter how much they try to keep dangerous microbes out of that bag, they can't seem to guarantee that they've caught every one.

This week, for instance, Dole Foods recalled thousands of bags of lettuce after a few leaves from one of those bags turned up positive for Salmonella bacteria.

In a quest to find out why contamination remains a problem, and what companies are doing about it, I went to one of America's great centers of salad-greens production: the Salinas Valley of California.

I looked up a man who's in charge of making sure that many of those greens are safe to eat: Will Daniels, senior vice president for operations and organic integrity at Earthbound Farm, based in San Juan Bautista.

Earthbound Farm sells bags of ready-to-eat organic greens by the tens of millions. Six years ago, it was the central figure in a national food safety scare.

It sold some spinach that carried a deadly microbe: E. coli O157:H7. The spinach went all over the country. It made at least 200 people sick. Three people died.

"I was at the center of the investigation and really took it very hard," says Daniels. "It was just a real tough time to go through, and something that I don't ever want to go through again."

But making sure it never happens again is really hard because, despite an intensive investigation, no one knows exactly what caused it to happen the first time. "There was no smoking gun, if you will," says Daniels.

Investigators found E. coli bacteria that matched the microbes that were making people sick on a ranch that was one of Earthbound's suppliers. But those bacteria were in animal feces a mile from the spinach field, Daniels says, "with no clear indication of what caused the contamination from a mile away to get into the spinach field itself."

Fighting microbes, in fact, is a little like boxing blindfolded. You can't see those disease-causing bacteria, but you know that they're out there, in lots of places.

For instance, they could be in the small stream, lined with bushes and trees, right beside the lettuce field where Daniels and I are standing. "Deer might be moving through here; wild pigs might be moving through here," Daniels says, nodding toward the stream. "Small rodents, rabbits, squirrels, things like that." Where there are animals, there is animal feces, possibly with disease-causing E. coli or Salmonella.

Or, look across the valley at those hillsides. They're pretty, but watch out: Cattle graze there. Their manure could wash down into the fields, or drain into ponds that are used to supply water for irrigation.

And what if there are frogs in those irrigation ponds? They can carry disease, too.

"Unfortunately, it looks like every animal is suspect," says Bob Martin, general manager of Rio Farms, in King City, Calif.

Even birds. "Birds are a big issue! They carry human pathogens, and we can't put diapers on them. We can't dome our fields; there's nothing we can do, short of trying to scare them away," says Martin.

Yet after the spinach disaster of 2006, California's big-time sellers of salad greens knew they had to do something. So they got together and hammered out a whole catalog of rules for growers. The rules amount to a manual for building a kind of anti-microbial Berlin Wall around their fields of greens.

Keeping The Birds And Beasts Away

Some fields in the Salinas Valley now have fences. Almost all of them, like the one Daniels took me to see, are surrounded by a no man's land of bare dirt to help detect any animal traffic. "You would be able to see animal tracks coming across it pretty easily," says Daniels.

If tracks do show up, or actual animal feces, any leafy greens around that spot doesn't get harvested. Some buyers tell their suppliers to discard everything within five feet; others say 50 feet.

Lettuce fields now have to be separated from cattle pastures, and throughout the valley, next to lettuce fields, you see white plastic pipes. Inside those pipes are mouse traps.

And the birds? Vegetable buyers won't take anything from the area directly under power lines — because birds like to sit there. Even trees, next to fields, are considered suspect.

There's a lot of debate about how effective some of these precautions are. They probably reduce the risk of contamination, but they don't eliminate it entirely.

"When it comes to food safety, if it's grown outdoors, forget it, there's no such thing as zero tolerance," says Bob Martin. "And everybody knows that, except for some food safety personnel of the big food buyers."

Cleaning and Washing

That's not quite the end of the story. The companies that sell bagged greens, in particular, have set up a few more lines of defense.

The first is washing. Mark Borman, president of Taylor Farms, took me inside one of his company's salad-packing plants in Salinas. This facility handles 10 million pounds of produce every week. It feels like a giant refrigerator and smells like a swimming pool, because the wash water is heavily chlorinated.

Borman points to one of the giant washing machines and shouts over the noise: "It works just kind of like a Jacuzzi whirlpool, so it kind of sucks the product under the water, tumbles it around, adds agitation."

Taylor Farms has added something new to the company's wash systems: some chemicals, including propylene glycol and phosphoric acid, which make the chlorine more effective. The company calls it " SmartWash," and it's now selling the salad cleanser to other companies, too. The new system still probably can't kill all the microbes on every contaminated lettuce leaf. But tests show that it does keep wash water from spreading those microbes from one leaf to thousands of others. Some experts think such "cross contamination" helped cause the poisoned spinach of 2006.

That's one line of defense. Earthbound Farms, being organic, can't use this new system yet. It uses standard chlorine. But it does run an impressive testing program. It samples leaves from every bin of freshly picked lettuce or spinach, and it also takes samples from the washed greens that are ready to ship.

"It is a true test-and-hold program, so we have to wait to get the negative results before we put it on a truck. Any positives go to the landfill," says Daniels.

There still are positives. Not very often, but every five weeks or so, one of these tests catches a sample that's contaminated with disease-causing E. coli or Salmonella.

It's impossible to test every leaf, so it probably means that some contaminated lettuce or spinach leaves are getting through. But the sampling program should catch any major contamination.

Ultimately, that's what these systems — the barriers around fields, better wash systems, testing programs — are supposed to achieve. They can't prevent every isolated case of contamination, but they are supposed to make sure that there are no more big, nationwide outbreaks of disease among people who chose to eat that healthful salad.

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Dan Charles is NPR's food and agriculture correspondent.