Junkfood Science: What if it never was the tomatoes?

June 27, 2008

What if it never was the tomatoes?

How were tomatoes pinpointed as the source of the latest salmonella outbreak that, as of today’s count, infected 810 people across the country between April 10th and June 15th? Nearly 2,000 tomato samples across the country and in Mexico have been tested and not a single tomato has been found to be contaminated with salmonella. The FDA has cleared 41 states and most of Mexico from being a source of tainted tomatoes.

What if tomatoes never were the source?

More than a week ago, there was a tiny footnote in a New Mexico news story that hinted at another source that made a bit more sense, but there has yet to be any notice of it. Before revealing that, let’s review the background on this outbreak, a bit of science, and how the source of foodborne illnesses are tracked down.


It will hopefully be reassuring to know that no new salmonella cases have been reported since June 15th. The growing numbers being reported in the news are because state laboratories are completing their previously submitted testings and state health departments have been testing more people in response to the outbreak, according to the Centers for Disease Control and Prevention.

The FDA’s Center for Food Safety and Applied Nutrition has a special website that is being updated daily, with news and everything you might want to know about the recent salmonella outbreak.

As frightening as 810 people getting sick is, it pales to the 40% of Americans who died from diarrhea and enteritis in 1900, just before our Grandparents were born. Back then 142.7/100,000 people DIED from foodborne illnesses — a rate that would equate today to nearly half a million people a year. Our food is 100 times safer today, as modern food production has incorporated science, sanitation, and safety practices at each step in the food processing to help protect us. The FDA randomly tests samples of produce, domestic and imported, from various growers, packers and shippers to identify lapses in safety procedures.

No food producer, organic or conventional, can ever provide sterile food, though. As the USDA’s Food Safety and Inspection Service (FSIS) has reiterated throughout this episode, there is also no valid scientific support that any type or source of such products (organic, free-range, Kosher or natural) is lower in salmonella. Over recent weeks, some organic or local growers have claimed their foods were safer, but there’s no evidence that smaller farms are inherently more immune to contamination, said Martha Robert, a microbiologist at the University of Florida Institute of Food and Agricultural Sciences and a safety adviser to the Florida Tomato Growers Exchange and the Center for Produce Safety at the University of California. “Mistakes can happen along the line with any size farm.” In fact, large packers are extremely stringent with sanitizing techniques and measures to prevent cross-contamination, where sometimes a small grower has been doing the same thing for years, she said. The key is that everyone is following good safety practices.

Helping to keep safe

But, what may be surprising, is that we play the biggest role in the food chain when it comes to preventing foodborne illnesses. As the CDC reports, 55% of foodborne illnesses are due to people not washing their hands, contaminating food during preparation, not cooking food properly and drinking raw milk. There’s a reason our Grandparents cooked most homegrown produce; or processed it with high amounts of sugars, salt and vinegars, to kill bacteria and reduce illness. The increasing popularity of fresh and raw foods today comes with added responsibilities on our part and an understanding of the risks. Food doesn’t come from nature sterile.

Salmonella been known as the most common cause of foodborne illness since first identified by Dr. Daniel E. Salmon more than 100 years ago. There are over 2,300 serotypes of the bacteria, according to the FSIS. Salmonella lives in the intestines of humans and animals and is commonly found in raw foods of animal origin, including chicken, eggs, fish, and dairy products, as well as produce. [That’s why consumers, especially anyone with a compromised immune system, infants, elderly and pregnant women, are urged not to eat raw protein foods.]

The bacteria can also contaminate other foods and surfaces that come in contract with it, which is why safe food handling is important. The FSIS, CDC, FDA Center for Food Safety and Applied Nutrition, Extension Services and other websites offer simple food preparation techniques that can help us keep our food safe. And the Be Food Safe for Consumers brochure, with four easy steps to safe food handling is available here.

Tomatoes have been identified as a source for salmonella infections since 1990, according to the CDC, with nine outbreaks between 1990 and 2004. Although the source has been found most times, the source for foodborne illnesses isn't not always identified.

The University of Florida Institute of Food and Agricultural Sciences wrote a consumer guide early on in this Salmonella outbreak linked to tomatoes, which can be downloaded here. You can’t tell by looking or smelling tomatoes if they’re contaminated, they say, but it’s best to avoid fruit with soft rot or damage; and store them in the refrigerator until needed. Wash produce but don’t soak it in water, although that won’t remove salmonella that may have gotten inside the produce. They also described the agricultural practices that have been instituted by the produce industry to reduce contamination.

Consumer alerts

A point that was never widely reported during this outbreak is that salmonella is easily killed with normal cooking, at temperatures above 150 degrees, as Al Wagner, Jr., Extension Food Technologist with the Texas Agricultural Extension Service noted. But we never heard advisories to simply cook tomatoes — even though roasted and grilled tomatoes, tomato sauces, and baked tomato dishes are quite delish.

At the FDA’s media briefing nearly two weeks ago, Dr. David Acheson, Associate Commissioner for Foods, was asked by one reporter if tomatoes could be safe if they were simply cooked. He replied that the science shows salmonella is easily killed with cooking. “There’s no question that you can kill salmonella if you cook it,” he said. It’s just like why we cook chicken, eggs, fish, and lots of other foods that are regularly contaminated with salmonella, he said.

The FDA’s messages were “a question of what’s the simplest consumer message,” said Dr. Acheson. We felt the simplest consumer message was to tell consumers that cooking wasn’t the best solution because we couldn’t know that they would cook them adequately, he told the press. “It just adds another of potential confusion to consumers. Well, yes, you can cook it,” he said, but then they’d have had to explain for how long and how. “So we try to stick with the ‘throw it out’ message as being simpler.”

It’s a soundbyte world. Nuances take time. Not understanding science is costly. Had the government not taken that precautionary stance, consumers would likely have blamed them for not keeping them perfectly safe.

The FDA advised consumers to limit their raw tomato consumption to those varieties not linked to this outbreak (cherry, grape and on-vine) and to avoid eating the most common varieties — raw round, plum and roma tomatoes — from any sources that hadn’t been ruled out as a source of the contamination. Consumers, and even some of the media, quickly took that to mean all round and roma tomatoes were not safe to eat, and farm stores and markets had soon taken all round and roma tomatoes off their shelves.

Everyone’s been hearing “tomatoes and salmonella,” said a spokeswoman for the Florida Department of Agriculture and Consumer Service. Perception is everything.

Amidst the fear and messages to avoid eating the most common varieties of fresh raw tomatoes, millions of pounds of tomatoes have been destroyed and the tomato industry has been devastated. Florida’s $500-$700 million industry and its tomato farmers, alone, have continued to endure unfathomable economic losses, even after their entire crop has been certified by the FDA as safe to eat. Farmers are now wondering how long it will be before tomatoes won’t be viewed as rotten by the public.

Did tomatoes get a raw deal?

We may never know the source of this latest outbreak, but maybe it never was the tomatoes. Readers may find it interesting to learn how public health agencies track down the source of foodborne illnesses. It’s detective work and exemplifies epidemiology in action.

As the FDA explains, when a person gets sick and goes to the doctor, foodborne illnesses are reported to the local health department. State labs test stools and look for pathogens with DNA fingerprints that are common among all of the people who got sick. If they find the same foodborne bug made all the people sick, the sickened people are interviewed and asked about everything they ate before they got sick. The epidemiologists then they look for a food they’d all eaten in common and the hunt begins for the source of that tainted food.

On May 22nd, state departments of health and the CDC announced that there had been an outbreak of salmonellosis in New Mexico and Texas, and the sick people were all positive for the Salmonella SaintPaul strain. They said the illnesses had been linked to round, plum and roma tomatoes.

Public warnings went out and investigators got busy trying to find the source of tainted tomatoes. People who subsequently got sick were, no doubt, especially asked if they’d eaten any tomatoes before they got sick (recall bias).

Did you just catch that?

Yes, this outbreak is clearly diagnosed as a salmonella SaintPaul infection, because all of the people have tested positive for this bacteria in their stool or blood. But the link to the tomatoes came from asking them what they had eaten and looking for a food that they had all eaten in common. Not a single tomato was or has yet been found to actually test positive for the bacteria. That’s what the FDA and health departments have deployed all possible resources trying to do for more than two months: find a tomato that is actually contaminated to confirm a link so they can begin other testing to find the cause.

As the University of Florida Institute of Food and Agriculture Sciences noted, about 30% of Americans eat tomatoes on a daily basis. And the most commonly eaten tomatoes are round, plum and roma. As of today’s count, about one out of every million people who eat tomatoes has gotten sick.

Do you think that every contaminated tomato has been eaten and not a single one has remained in anyone’s kitchen or any grocery store across 36 states, in any delivery truck, packing and distribution center or farm in the country or Mexico, even though testing in earnest had begun in May and hundreds of people were getting sick through mid-June? Yes, it's possible that the errant tomatoes have still gone undetected, but the longer this goes on, the more unlikely that sounds and the more likely the case is to go cold.

Or, could there be a confounding factor — something that shares an association with tomatoes — that might point to another food these people ate along with tomatoes?

It’s been a week since a tiny footnote appeared in a news story with a comment made by a public health nurse at the Indian Health Services that suggests just that. Data collected by her team and other New Mexico health officials “led the state Department of Health to draw a prompt conclusion that tomatoes were the source of contamination,” the Albuquerque Journal reported. This was the origin of tomatoes being linked to the nationwide outbreak of salmonella.

The Navajo reservation had the highest concentration of state residents who came down with this rare and virulent strain of salmonella early on. The very first case in the country is believed to have been treated in Gallup, New Mexico. “We always jump when there is something unusual,” said Kimberlae Houk, a 24-year veteran epidemiologist and public health nurse at Northern Navajo Medical Clinic in Shiprock.

As the Albuquerque Journal reported on June 20th:

Salmonella Saintpaul hammered the Navajo Nation, which claimed at least 30 percent of the 78 New Mexicans who were sick, a state Department of Health official said. The reason for the concentration of illnesses at the Navajo reservation remains a mystery, said Paul Ettestad, the state's epidemiologist. "I'm not sure we're ever going to know why such a high proportion of cases come from the Navajo reservation," Ettestad said Thursday.

Tests on tomato samples by New Mexico and other states have so far turned up no evidence of the source of the salmonella outbreak... Technicians have tried for weeks to grow salmonella cultures from tomato samples purchased randomly at stores. "Nobody's been able to do it yet."

New Mexico health officials have a long history of experience with dangerous diseases, such as Hantavirus and plague. Houk told the Journal that IHS workers applied many of the same epidemiological techniques to investigate the salmonella outbreak. “Our job is to drop whatever we're doing and take care of a communicable disease,” she said.

Much of that job involved performing detailed surveys to determine what foods salmonella patients had eaten in the week preceding the onset of symptoms, Houk said. Many people lack telephones on the Navajo reservation, requiring health workers to drive huge distances to administer the surveys. Similar techniques have been used to identify the source of Hantavirus, plague, measles and other diseases, Houk said.

On May 23, Houk said she informally polled about a dozen nurses at the Shiprock clinic about which food might have caused the outbreak. "Half the nurses thought it was tomatoes and half the nurses thought it was lettuce," she said.

Officials went with the tomatoes.

Lettuce and tomatoes, they go together as a side with practically every Southwest dish and most raw tomatoes are most often eaten as part of a lettuce salad. Lettuce is also pulled up from the ground where salmonella can persist in the soil and the roots are suspected as being especially attractive to the bacteria. Lettuce has lots of little creases and crevices that make it harder to clean, it’s often soaked in water baths to refresh it prior to shipping or selling which can absorb the bacteria into the leaves. And in the past 35 years, the CDC reports that leafy greens are a growing source for foodborne disease outbreaks, accounting for about 6.5% of illnesses, with 10% caused by salmonella. It’s a challenge that they’ve already identified at this year’s International Conference on Emerging Infectious Diseases in Atlanta, Georgia, and are busy working on.

Or, is it another ingredient in salsa, guacamole or pico de gallo, or something else also enjoyed in Southwest dishes? This detective story isn’t over yet.

But, the FDA has confirmed that these states and countries (practically everywhere we get tomatoes) are not a source of contaminated tomatoes, and their raw plum, raw roma and raw round tomatoes are safe to eat:

It’s tomato season and tomatoes are back on my menu -- although, between us, they never left, in some form. :-)

© 2008 Sandy Szwarc

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