Can Contamination Be Controlled?
E. coli outbreaks in fresh produce coincide with the push for volume, variety and year-round supplies.
Thursday, June 19, 2008
Just after 9 on a frigid January morning in 2007, nearly six months after the disastrous E. coli outbreaks in bagged spinach, some 200 vegetable farmers and shippers, tailed by a small army of reporters and a few trial attorneys, filed into an open-air auditorium on the Monterey County Fairgrounds.
The occasion was a hearing before the California Department of Food and Agriculture, and the lone item on the agenda was food safety. Monterey County is in the heart of the Salinas Valley, a vast and fertile plain billed as the nation’s salad bowl but now known as the new ground zero for E. coli.
Since 1995, more than half of all major produce outbreaks of E. coli O157:H7, and nearly all lettuce and spinach outbreaks, including those in 2006, were traced to farms or packing sheds in the Salinas Valley. The result, as Jim Bogart, president of the Grower-Shipper Association of Central California, told the audience at the hearing, is “a crisis of confidence in our industry that extends throughout the consumer marketplace.”
To restore that confidence, the produce industry launched a zero-tolerance program to eliminate pathogens through voluntary measures by producers themselves– an idea that most of those in the auditorium seemed to support. “If we are talking about how farmers should farm,” declared Tom Nassif, head of the trade group Western Growers, “they know better than any regulators.”
Nassif ’s perspective is not exactly the mainstream view. Although it’s clear that vegetable producers are genuinely and desperately interested in halting outbreaks (spinach growers alone suffered $200 million in lost sales in 2006), there is a growing consensus outside the industry that the crisis may already be beyond growers’ ability to fix.
Despite the media’s focus on the feral pigs as the killer vector in the spinach outbreak, for example, researchers have identified dozens of other “nodes of risk” where pathogens could have breached the industry’s safety systems. And, as with the meat business, many of those nodes were created by the very technologies and business practices that allow the industry to deliver ever-greater volumes of produce year-round at declining costs.
“These guys are in supply-chain mode,” says Trevor Suslow, a University of California at Davis microbiologist and a leading expert in food-safety investigations. “And when you’re in that mode, when your objective is to fill orders, you tend to stretch your system– in terms of capacity and throughput, but also in terms of what you can really handle while paying attention to all the details of quality and safety.”
The gist of his critique is something even industry insiders no longer dispute– namely, that the upward curve of fresh produce outbreaks began in the 1980s, just as grocery retailers began pushing suppliers for larger volumes, more varieties, and year-round coverage.
TECHNOLOGY ALLOWS FOR GREATER YIELDS, BUT PROCESSING THOSE MASSIVE HARVESTS IN HUGE QUANTITIES CAN OPEN UP GREATER POSSIBILITY FOR CONTAMINATION.
To satisfy this huge new market, growers had to reengineer the produce business: they not only created a massive reciprocal network of farms in different growing zones– from the Salinas Valley to Arizona to Mexico and even to South America– that could generate a continuous volume 12 months out of the year, but they significantly expanded production volume within those zones, and nowhere more dramatically than in the Salinas Valley.
Some of that new volume has come from better farming methods: planting crops more densely in the field, for example, or harvesting more crops per season (each crop of baby spinach is ready in just 26 days); and by using mechanization: leafy greens that were once laboriously hand-picked are now carefully mowed by huge harvesters, which in turn allowed farmers to plant ever larger seedbeds. But much of the new output has come the old-fashioned way: by adding new acres.
And while some of these new acres would be found elsewhere, like Arizona or Mexico or Chile, there was considerable economic pressure to look for new acres in existing produce-growing regions, such as the Salinas Valley, where growers could exploit an existing processing infrastructure and an existing labor pool.
And it is here, says Suslow, that the problems may have begun. Because the Salinas Valley is already crowded with farms (and under new pressure from encroaching urban development), expansion meant growers had to leave the traditional farming areas on the flat valley floors and move into the surrounding foothills, which, unfortunately, were already occupied– by cattle and dairy operations and by wildlife habitat– with the result that “suddenly, you have produce fields surrounded by cattle and feral pigs.”
It’s probably not a coincidence that the spinach field identified as the source of the E. coli O157:H7 strain found in bags of contaminated Dole spinach was not only next to a Salinas Valley cattle ranch but was itself a cattle pasture only a few years earlier.
In the mainstream press, explanations for this collision of farms, ranches, and wildlife follow what Rob Atwill, another UC-Davis researcher, calls the Typhoid Mary theory: namely, that a specific carrier– a feral pig, say, or a stray cow, or even a bird– picks up the E. coli from cow manure on a nearby ranch, and then “runs through the field and craps.” And in fact, the fresh produce industry very much hopes this is how the contamination occurred, because it means that the problem can be prevented, or at least minimized, through efforts to keep critters out of the fields– building stronger fences around them, say, or by setting animal traps or offering cash bounties to hunters who shoot feral pigs– all of which the industry has begun doing.
Unfortunately, there are any number of other ways contamination can occur, most of which are far harder, if not impossible, to control. For example, Atwill has been tracking a theory known as winter migration, which suggests that during the heavy winter rains, the pathogen washes from its natural reservoirs (such as cattle pastures) down the hillsides and into the valley below. “If you look at the terrain,” says Atwill, “it’s clearly demarcated: you have the foothills, and then the plains, and linking them are all these historic streams that have either been left intact or else canalized to run next to the farm fields.”
Once a pathogen enters this massive drainage system, it has access to the agriculture complex through thousands of fixed points, such as irrigation wells, canals, and ditches– a massive pathogenic opportunity that modern growing methods are actually making even worse. Because the new large seedbeds are too wide for traditional drip or furrow irrigation methods, Salinas Valley farmers use overhead sprinklers, which means that if E. coli infiltrates the irrigation system, farmers are simply spraying pathogens right on the leaves. What’s more, once E. coli O157:H7 enters the watershed, it can access farm areas not only via known entry points, like irrigation systems, but through the nearly infinite number of nonpoint sources, like riverbanks or flood areas. Researchers have found E. coli O157:H7 at edges of rivers and streams, hiding in clay, or on rocks in large, slime-covered microbial colonies. During floods, overflowing rivers can carry these pathogens onto roads and into adjacent fields. Because of such nonpoint risks, many big distributors now reject any produce grown in a recently flooded field.
DUST LADEN WITH E. COLI O157:H7 CAN TRAVEL NEARLY ANYWHERE.
Yet even these measures get at only part of the risk, because although E. coli O157:H7 is clearly using water systems and flooding to migrate, the bacteria don’t need water to move. While many bacteria populations die off once soils dry out, E. coli O157:H7 will tolerate weeks and even months of dryness. Such drought tolerance means that E. coli O157:H7 can not only survive in dry dirt, but can aerosolize, or become airborne on dust particles, which significantly increases the pathogen’s range– and could seriously undermine the industry’s efforts to protect the supply chain. Atwill says dust laden with E. coli O157:H7 can travel nearly anywhere: it could be carried by wind from a dry streambed, for example; it could be kicked into the air by a cow stomping its own dried manure; it could be thrown from a dirt road by a passing vehicle.
“All you need is a delivery truck driving down the dirt road next to a pasture, stirring up the dust and letting that dust cloud move downwind and deposit itself in the middle of a field of leafy greens.”
If the winter-migration theory is correct or, more likely, if the cause turns out to be some combination of winter migration and Typhoid Mary or some other vector still to be conjectured, prospects for fixing the problem suddenly become far less certain. Fencing against dust isn’t practical, nor is securing every inch of the hundreds of miles of streambeds and canal banks that run through the Salinas watershed.
Worse, once a pathogen enters a field, the industry has no assured means to keep the bug from reaching consumers. Unlike their counterparts in the meat business, fresh produce processors have no kill step– processors cannot subject greens to steam washes nor reasonably expect consumers to boil their salad mixes. And while such risks have always been present in fresh produce, they’ve actually been magnified by many of the same improvements the industry undertook to increase its output and lower its costs.
The huge mowing machines that growers rely on leave cuts on the spinach and salad greens– wounds that not only provide the E. coli O157:H7 with a place to attach itself but also give it a source of nutrient-rich leaf juice. And as soon as E. coli begins to feed and replicate on the leaf, it is given the perfect opportunity to spread its progeny: the freshly harvested greens are mixed with hundreds of pounds of other greens and thousands of gallons of water in the processing plant. This procedure not only provides E. coli with lots of moisture, which it craves, but it also gives the germs virtually unlimited opportunities to touch, and potentially contaminate, other freshly cut leaves.
Processors work hard to interrupt this pathogenic cascade: spinach and other greens are sent down huge water-filled flumes to physically dislodge the bacteria, then dunked in chlorinated water, then kept in refrigerated warehouses, trucks, and display cases until the consumer buys it. But these measures are proving insufficient against the newer strains of E. coli. Once tucked inside the cut edge of the plant, the pathogen is formidably difficult to shake free. And although chlorine kills E. coli as it floats in the water, the chemical can’t always kill those pathogens still lodged on plant surfaces. This is especially true with the low chlorine concentrations that processors often use in order not to affect the odor or flavor of the greens, according to Robert Mandrell, a microbial expert with the USDA’s extension service in California and one of the top federal experts on E. coli and produce. All told, Mandrell said, the washing process is “hit and miss.”
Even the industry acknowledges that washing “removes between 90 and 99 percent of all pathogens.”
Refrigeration is also proving less and less effective. Older forms of E. coli suffered in cold temperatures, but newer strains can tolerate the “cold chain” quite well.
“In school, you learned that E. coli wouldn’t grow in temperatures below 45 degrees,” Suslow recalls. “Well, it can clearly grow– it just grows slowly.” Slowly, that is, until the pathogen encounters what food microbiologists call “temperature abuse”– a temporary gap in the chain of refrigerated storage or transport between the processor and the consumer. Perhaps the bagged salad sits too long on a loading ramp; maybe a consumer leaves it too long in a warm car or on a kitchen counter. Once temperatures reach an optimal level for the pathogen, the bug starts reproducing rapidly. And because warm temperatures accelerate the process of leaf decay, the decomposing greens begin to emit nitrogen, another key nutrient for E. coli– all of which, Mandrell says, helps explain why even a short bout of temperature abuse can yield a tenfold increase in the pathogen load.
Recognizing these vulnerabilities, the industry is responding with better technologies. Earthbound Farms, the largest producer of organic salads and spinach– and the source of one of the 2006 outbreaks– now uses extremely sensitive testing methods to examine produce samples. Greens are tested before they’re washed and after they’re packed, and they’re held in storage until the test results are known. “We’ve completely reinvented our food safety protocol,” a company spokeswoman told me. “No one else is doing anything like this.”
Yet it is possible that E. coli is eluding even these sophisticated methods. Suslow, Atwill, and other researchers now suspect that in some cases, the initial contamination in the farm field occurs at such low bacterial concentrations and is so unevenly distributed that the pathogens may simply not be detected during routine sampling. Only after conditions have begun to improve for the pathogen do its numbers begin to multiply. What all this has led some researchers to conclude is that tiny doses of E. coli, under the right conditions, could be reaching infectious concentrations just as the product is reaching the consumer.
What’s more, for all the industry’s efforts to prevent such a scenario from ever occurring, most of the trends now transforming that industry actually make such a scenario more likely. The emphasis on rapid delivery, for example, means produce is usually picked, packed, and on its way to a customer in 72 hours or less, and often in less than 36 hours. The massive consolidations that came about as the industry cut costs lower and lower meant that smaller, less efficient farms had to give way to larger, integrated operations in which huge factory farms feed their output into enormous centralized packing houses. And while this growing consolidation and integration has helped drive down the retail costs of your fresh salad, it has also made the task of keeping pathogens out of that salad considerably harder.
Given these realities, one begins to understand both why outbreaks keep occurring and why the regulatory response has been so tentative. For all the legislative hearings and the threats of tough new laws, state and federal agencies, especially the Food and Drug Administration, which has authority over fresh produce, have been slow to offer any dramatic proposals for fixing the system.
The only sure protection from preharvest pathogens would be to require that all produce be grown in greenhouses– an enormously expensive solution that no politician would even consider. Yet the alternative– mandating changes in traditional farming practices– is no more attractive because no one is exactly sure how the pathogens are entering the supply chain and, thus, which practices should be encouraged or prohibited.
Federal agencies have been more or less content to let the industry develop its own fixes, in the hopes that market pressure will force the necessary changes. Yet the flaw in this solution may be its expense. Each improvement in safety, from better testing and stronger fences to rodent traps, sonic cannons, and new irrigation systems– all add costs to what is already a low-margin business. Farmers might be willing to make such investments if they could be assured that spending more money would get them a higher selling price.
But safety isn’t an added value that consumers feel they should have to pay more for, and so there is no way for retailers to easily pass on the extra costs to consumers, which makes the retailers much less willing to accept higher prices from their suppliers. Add to that the fact that, statistically, most outbreaks are never successfully traced back to a particular farm or even officially confirmed.
In the meantime, more acres are planted. Growing seasons are stretched to get one more crop in before winter.
“You have to be running all the time, with something being planted, harvested, or packed, year round,” says Suslow. “Under a different scenario, a company might say, ‘We need to wait until this field dries out a bit, because we don’t want to be taking this heavy equipment into a rain-soaked field, because it makes everything more difficult– makes harvest more difficult, it kicks soil onto the product.’ ” But because the current scenario is one in which companies must maximize output, Suslow says, they are more and more likely to press ahead in less than optimal conditions, thereby “making all of the things they have in place to meet their quality and food safety expectations more difficult.” Sometimes, Suslow told me, “you just want to say, ‘I can’t believe you’re harvesting right now.’ ”