SPECIAL REPORT
Unfinished Business:
Preventing Future E.Coli 0157 Outbreaks

By Dr. Charles Benbrook


Since last fall’s E.coli outbreak, everyone has been focused on how to prevent another outbreak. The good news is that growers and processors, especially in California, have adopted significant, new prevention-based food safety practices. A set of Good Agricultural Practice (GAP) metrics for growers and processors has been developed by a coalition of industry and farm organizations.

Fresh Express, a major lettuce and spinach processor, has recently provided $2 million to fund nine studies focusing on the prevention of E. coli O157 in leafy greens. Projects are focusing on the ability of E. coli O157 to become internalized in lettuce and spinach, the possible role of insects in transmitting pathogens and environmental factors increasing the risk of extended survival or regrowth of foodborne pathogens.

Natural Selection Foods (NSF) processed the Dole brand baby spinach on August 15th that triggered the 2006 outbreak. The company’s cooling, washing and bagging procedures came under intense scrutiny as state and federal investigators searched for the cause of the outbreak. The effort to find where and how the E. coli O157 got into the raw spinach in the field was equally intensive and went on for over six months.

Within weeks of the outbreak and its own investigation of the outbreak, NSF dramatically increased preventive measures, expanding their testing of production inputs for pathogens to encompass seeds, irrigation water, composts and other soil amendments. All water used in production is now tested weekly to monthly for enterohaemorrhagic E. coli and Salmonella. The environmental conditions in and around fields are assessed to identify and avoid possible sources of contamination. More and more in-depth field audits are routinely performed.

There were even more significant changes in NSF processing plant procedures. In the fall of 2006, two “firewalls” were added to their food safety system; the first “test and hold” firewall applies to raw product as it enters the plant, the second after product is washed, bagged and ready to ship. NSF now tests all incoming loads of raw product for enterohaemorrhagic E. coli (including O157:H7) and Salmonella and holds the greens until the results confirm the absence of pathogens. Thus far, pathogens have been found in about three dozen lots of raw produce, representing about one-tenth of 1 percent of the total pounds of raw product tested. These lots have been destroyed.

The second firewall focuses on fully processed and bagged product that is ready to ship. Samples from all lots are tested and held, and shipped only after results confirm the absence of pathogens. Thus far, no lots of finished product have tested positive, evidence that the dual-firewall approach is working.

E.coli: The Big Picture
The scope of the problem, however, remains sobering, as does what it will take across the industry to prevent future outbreaks. Other strains of enterohaemorrhagic E. coli cause tens of thousands of cases each year and Salmonella causes many more cases than all strains of E. coli combined, but far fewer cases leading to serious, life-threatening complications.

The fall 2006 spinach outbreak led, according to the FDA, to 204 illnesses. The California Department of Health Services recently reported that 162 of the individuals who suffered illnesses reported eating spinach and 151 reported eating bagged spinach. While most of the spinach that was found to contain the outbreak strain of E. coli O157 was Dole spinach, other brands were implicated in the outbreak. For many cases, the brand was not known.

Given the press attention devoted to the fall outbreak, one would think it accounted for a significant share of last year’s E. coli O157 illnesses. Not true.

Based on the most recent FoodNet data, about 52,000 cases of E. coli O157 illnesses were expected in 2006 (down 29 percent from 73,000 cases in 1999). The CDC attributes this encouraging reduction in cases since 1999 to progress in reducing illnesses caused by undercooked hamburger.

Foodborne sources of E. coli O157 likely accounted for about 50 percent of the total number of outbreaks in 2006 according to the CDC, with produce representing an estimated 21 percent, or 5,460 cases. The 204 cases triggered by the 2006 spinach outbreak thus represent fewer than 4 percent of the total number of produce-triggered cases, and less than half of 1 percent of the 52,000 illnesses expected in 2006 from exposure to E. coli O157.

The big picture reveals that the spinach outbreak was a small part of a larger problem of bacterial contamination. Because of the significant health risks posed by these bacteria, they must become the focus of monitoring and prevention efforts.

Widening Margins of Safety
The fastest way to substantially broaden margins of food safety will depend on a systematic, farm to fork approach. Success will depend on progress in three areas:

1. Reduce Pathogen Loads. Track the pathogens to their source, understand
the conditions in which they thrive and change those conditions. This approach is logical and proven, yet is barely on the radar screen of industry leaders or government regulators. A mountain of data and experience with foodborne illness outbreaks linked to fresh produce points to proximity of production fields to cattle operations—and manure—as a significant risk factor for E. coli O157 contamination. Cattle and crop farming have co-existed on the same farms and in the same regions for hundreds of years with few E. coli O157 illnesses linked to consumption. But leafy greens marketed as ready-to-eat, fresh-cut product are uniquely vulnerable to foodborne pathogens for several reasons: it’s not usually cooked; the harvested portion of the plants grows very close to the soil; and, the packaging is an excellent environment for bacterial proliferation, especially if the cold chain is broken or if consumers do not respect the product expiration date. The unique vulnerability of fresh cut leafy greens calls for added measures to keep cattle, and their manure, well away from production fields.

2. Monitor, Study and Probe for Answers. More testing and more accurate test methods are needed. The GAP Metrics’ total reliance on generic E. coli water testing is a serious flaw and should be rejected by growers, buyers and the government. Innovative companies are already testing—and benefiting from—testing protocols focusing on E. coli O157, other pathogenic forms of E. coli and Salmonella.

The results of testing across farms, processors and regions, whether done by individual farmers and processors, regulators or researchers, need to be shared and analyzed by teams of experts to offer new insights. The government should offer financial support for testing, as long as accurate and verified methods are used.

3. Identify and Deal with High-Risk Circumstances. Moderate and high-risk fields need to be identified, based on past records and ongoing testing programs. In particular, fields within a half-mile of cattle or open range should be planted with crops other than leafy greens for the next few years as science sharpens understanding of the causes of O157 outbreaks. If such fields are used for fresh cut leafy greens, the raw product harvested from the fields should be processed only in conjunction with a raw product and finished-product testing program encompassing all pathogenic strains of E. coli and Salmonella.

Levels of risk associated with different sources of irrigation water will vary by orders of magnitude. It makes no sense to force growers to continue testing very clean water sources as frequently as those sources known to periodically bear possibly risky pathogen loads. Production inputs known to open the door to pathogens, or to encourage their growth, need to be flagged and matched with more intensive sampling and testing. Practices and inputs known to be helpful in preventing initial pathogen colonization in a field or suppressing pathogen growth also need to be identified and incorporated.

Tilting the Odds Against E. coli O157
Several studies have offered new insights that could help prevent future outbreaks. For instance, in one study using a water source spiked with E. coli, over 90 percent of the spinach plants were contaminated with E. coli O157 after being irrigated with a sprinkler system, compared to less than 20 percent of the plants under surface irrigation. Sprinklers result in more splashing onto leaf surfaces of water mixed with soil. Also, management practices such as reducing fungicide use and incorporating soil amendments that encourage diverse microbial communities on the leaf surface can slow or block the proliferation of E. coli.

Higher levels of phytochemicals expressed by plants grown in organic systems can also lead to direct suppression of E. coli O157. These plants have been shown to ward themselves of E. coli infections within days to a few weeks after infections. In addition, excessive levels of nitrogen fertilizer are known to increase the release of nitrogen compounds both through the root system and the leaf surface, possibly stimulating bacterial growth. Nitrogen is typically released slower in organic production systems, a factor that may emerge as a food safety advantage for organic production.

Only the highest quality production inputs should be used, especially composts and other soil amendments made from manure or other animal byproducts. Production inputs should be tested routinely to assure that finished compost is stable and pathogen free and remains so until incorporated into the soil in a production field.

Moving Forward
From farm to fork, multiple and redundant prevention-based practices should be implemented with more sensitive, specific testing at each step. Valuable new food safety measures pioneered and proven by one company, such as the NSF’s firewalls, should be quickly adopted industry-wide. Pursuing these and other new strategies can expand margins of safety significantly and quickly, and without driving up production costs to the point where no farmer or processor can stay in business.

With continued safety scares, trust in produce safety will decline enough to depress the average number of daily servings and, in turn, our collective public health. This is why the stakes are so high. Progress has clearly been made through coordinated efforts within the industry and individual companies have raised the food safety bar. However, the industry must continue to develop and fully implement strategies that will drive down E. coli O157 and other foodborne pathogen risks to as close to zero as possible, as quickly as possible.

Dr. Charles Benbrook is the chief scientist at The Organic Center. He has worked in Washington, D.C. on agricultural policy, science and regulatory issues and was the executive director of the Board on Agriculture of the National Academy of Sciences. You can reach him at cbenbrook@organic-center.org. This article was adapted from the full version, available at www.organic-center.org.