Unlike many foods, fresh produce such as leafy greens doesn’t have a kill step. “No heat or chemical treatment can eliminate microorganisms that might cross-contaminate fruits or vegetables,” says Bob Whitaker, PhD, chief science officer, Produce Marketing Association of Newark, Del., which provides connections and industry solutions to members of the fresh produce and floral industries. This means that rigorous food safety measures must be in place at every point in their supply chain.
Despite best efforts, however, human pathogens can get into the nooks and crannies of fresh produce where wash water can’t reach. Assuring the safety of fresh produce depends on preventing contamination throughout the produce supply chain, from farm to fork. “This can be a challenging task given that most fresh produce is grown outdoors, where it may be exposed to environmental contaminants in the soil, air, water, and wind,” says Jim Gorny, PhD, senior science advisor for produce safety, FDA Center for Food Safety & Applied Nutrition, College Park, Md. “Therefore, it’s essential to ensure that agricultural inputs such as agricultural water and soil amendments are as free of human pathogens as possible and that food contact surfaces that touch fresh produce, such as hands and conveyor belts, don’t become a means of produce contamination.”
Challenges in Investigating Fresh Produce Outbreaks
Considering that about a billion servings of fresh produce are consumed daily, the number of foodborne illness outbreaks (correlated with the rate of contamination) is remarkably low, says Jennifer McEntire, PhD, vice president of food safety and technology, United Fresh Produce Association, a Washington, D.C.-based national trade association representing the fresh produce supply chain. According to CDC, fresh produce accounted for 17 percent of outbreaks from 2008 to 2015, causing about 1,200 illnesses per year.
But the year 2018 challenged the U.S. food industry to reconsider whether produce safety practices are indeed reasonably effective at preventing a single contamination event from occurring when two E. coli outbreaks and a Cyclospora outbreak in the U.S. were traced to romaine lettuce and were reported in April, July, and November, respectively.
Outbreaks often perplex federal health officials as to how and why they originated because during an outbreak investigation, they respond to a failure in food safety measures somewhere within a large number of potential points between the farm and consumer. “At many points in the supply chain, the food from several sources could mix, which makes the traceback investigation far more complex,” Dr. Gorny says.
“Even if the traceback investigation leads to a common food source or several potential sources, it’s possible that harvesting or processing may have ceased. In the case of perishable commodities, such as leafy greens, there may not be any product left in the marketplace or in consumers’ homes to test,” Dr. Gorny continues. “Therefore, by the time an epidemiologist identifies a potential food source, many of these products have passed their expiration dates and are no longer available, making it much more difficult for investigators to collect the necessary information to help identify a source.”
To further complicate matters, investigators might have to cover hundreds of acres of farmland or thousands of square feet in a processing facility. When multiple farms are potentially involved, the investigation area could be spread over many miles. “Essentially, investigators are looking for invisible bacteria, much like looking for a needle in a haystack,” Dr. Gorny says.
Focusing on Traceability
Following the large leafy green multistate outbreaks of the mid and late 2000s in the U.S., the produce industry voluntarily worked to develop the Produce Traceability Initiative to develop a standardized industry approach to enhance the speed and efficiency of traceability systems for the future. “This voluntary approach is a great start because it allows the industry to align the way it collects and uses data based on Global Standards One (GS1) US, which sets standards for global commerce; it works toward case-level traceability,” says Ben Miller, PhD, MPH, senior director of food safety, The Acheson Group, a global food safety consulting group in Northfield, Minn.
FDA strongly encourages the leafy greens industry to adopt traceability best practices and state-of-the-art technology. This would ensure quick and easy access to key data elements from farm to fork when leafy greens are involved in a potential recall or outbreak. “Leafy greens are a highly perishable commodity; traceability information should facilitate the rapid tracking of involved product throughout the entire supply chain to expedite its removal from commerce, prevent additional consumer exposures, and properly focus any recall actions,” Dr. Gorny says.
A key element that would assist tracing efforts during an outbreak is the ability to identify specific farms or ranches that contribute to production lots, especially when the product has been comingled. While it’s important to identify where a product was grown and not simply the location of the business entity that shipped or processed it, it is equally important to be able to determine which specific farm(s) and growing region(s) are responsible for supplying the contaminated product. “This information is crucial to developing accurate public health messaging to protect the public from exposure and empower consumers to take appropriate actions,” Dr. Gorny adds.
United Fresh Produce Association and Produce Marketing Association, with input from the Romaine Task Force, are leading an initiative to include voluntary labeling on all romaine lettuce packaging that identifies its origin and a means to determine its harvest date. “Having this information will improve our ability to provide more targeted information to consumers during an outbreak,” Dr. Gorny says. “Significant progress has been made by the lettuce and leafy greens industry to assure moving forward that the growing region is clearly and uniformly labeled on romaine lettuce products.”
Without the ability to identify the growing region or specific suppliers of suspected shipments, public messaging by FDA and other public health partners during recalls or outbreaks is broad out of necessity, possibly implicating farms and growing regions that aren’t responsible for the contamination. “If supplier data are maintained when a product is comingled, it is easier to narrow the number of suspected shipments and suppliers of the contaminated product once it has been processed,” Dr. Gorny says.
But Dr. Miller doesn’t foresee improvements in supply chain traceability unless there’s a regulatory requirement. “Distributors and retailers don’t have an immediate financial reason to maintain case-level traceability, so it’s likely that the FDA will need to address this through authority granted under its Food Safety Modernization Act [FSMA] of 2011 before we see full supply chain traceability,” he says. “Essentially, supply chain traceability is no longer a technology problem; rather it’s a political and policy problem.”
To improve the traceability process, Dr. Miller believes that blockchain technology holds promise but will require operational changes in the supply before it’s fully effective. “Blockchain technology creates the ability to accurately associate transactional data across the supply chain. Companies such as distributors would have to make operational changes that would capture case-level data as shipments are received, pallets are broken down, and orders are filled for outgoing shipments,” he says. “But without operational changes like these, more integrated data systems will continue to capture data that lack the detail and granularity that public health investigators need to rapidly trace an outbreak and possibly prevent ongoing illnesses.”
Eyeing Water Safety
In addition to efforts to make it easier to identify sources of foodborne illness outbreaks, research is being conducted on how to prevent contamination from occurring in the first place. One aspect that is currently being studied is ensuring that water sources that come into contact with leafy greens are safe.
Lettuce producer and manufacturer Fresh Express formed a panel of independent scientific, production, and policy experts in November 2018 to make recommendations for new or improved ways to prevent Cyclospora outbreaks. Michael T. Osterholm, PhD, MPH, chair of the Fresh Express Blue-Ribbon Panel on Prevention of Cyclospora Outbreaks, who is also a regents professor, University of Minnesota, Minneapolis, says leafy greens outbreaks differ from other types of foodborne illness outbreaks because humans must play an essential role given that Cyclospora requires a human host to complete its lifecycle. The panel was formed as a result of 2018 Cyclospora outbreaks involving fresh produce grown and harvested in the U.S.
Cyclospora outbreaks since the 1990s have had high attack rates. “This suggests that contamination doesn’t occur sporadically, and that there’s a much more widely disseminated source for the parasite,” Dr. Osterholm says.
The parasite must live seven to 14 days outside of the human body to mature and be capable of infecting other humans. “If a parasite is excreted in a human stool, for example, it requires that time period to pass before it becomes infectious,” he says.
Given this information, the panel is looking to determine potential sources and preventive controls, including if water can spread Cyclospora. Dr. Osterholm surmises that water used for irrigation or spraying could be the culprit. Perhaps water could become contaminated from septic systems leaking into water sources.
“We need to make sure that there’s no intentional or unintentional release of human fecal material into waterways,” Dr. Osterholm says. “A number of actions could be implemented to reduce the potential for Cyclospora to enter water and to prevent water that contains the parasite from being used on plants. Because the parasite is highly resistant to chlorination, the chemical can’t be used to help solve the problem.”
On April 19, the California Leafy Greens Marketing Agreement (LGMA) Board adopted more stringent requirements designed to reduce risks related to water used in growing leafy greens. The updates include specific directives such as no longer allowing the use of untreated surface water for overhead irrigation of leafy greens prior to harvesting, says April Ward, MSc, communications director, California LGMA, Sacramento, Calif.
The new standards are in direct response to FDA investigations of last year’s E. coli outbreak involving romaine lettuce. Clues pointed to irrigation water from sources such as canals and reservoirs as a possible cause.
California LGMA devised the new water metrics by working closely with Western Growers, who coordinated a working group, and Arizona LGMA. The organizations looked at water sources and how they’re being used in production. “It’s unlikely that water from deep wells could be contaminated with human pathogens because the Earth provides an effective filtration process to eliminate bacteria,” says Dr. Whitaker. “Well water can therefore be used without fear of cross-contamination, provided the delivery system is well maintained and inspected.
“But surface waters such as ponds or canals are more likely to be impacted by runoff from pasture lands or animal operations, wild animals, wind-blown dust, or even septic systems—making it necessary that they’re evaluated and perhaps treated with disinfectants to manage potential pathogen contamination,” Dr. Whitaker continues.
“LGMA’s program has always required growers to test their water because it can carry pathogens,” Ward says. “But the new requirements include additional safeguards that ensure farmers categorize the water source and consider how and when water is applied to a crop; conduct testing to ensure water is safe for the intended use; and sanitize water if necessary.”
The new metrics will become part of mandatory government audits that comprise the LGMA’s food safety system. The LGMA will also begin an education and outreach effort to ensure that all members of the leafy greens community understand how to comply with the new standards, Ward says.
Other Efforts to Ensure Safety
Many other groups and organizations are also committed to improving leafy green safety. The CEOs of the United Fresh Produce Association and the Produce Marketing Association are co-leading a Romaine Task Force that includes a diverse group of industry thought leaders, FDA, CDC, trade groups, public interest groups, and academic scientists throughout the supply chain.
Following the 2018 outbreaks involving romaine, the task force is tackling key issues around produce labeling to allow consumers to know where their romaine was grown, permit supply chain-wide traceability, explore science-related issues around agricultural water and root cause analysis, and identify and prioritize improvements in the investigative process, Dr. Miller says.
“We expect to conclude our work this year and then reach across the entire supply chain to provide educational opportunities to ease the implementation of changes that will be recommended or create awareness around any new tools in development,” Dr. Whitaker says.
The Center for Produce Safety (CPS), which provides the produce industry with information on enhancing the safety of fresh fruits and vegetables, has prioritized produce safety research (including but not limited to leafy greens) for more than a decade. Nearly 150 research programs have been funded thus far, with an investment of nearly $26 million. Among the research priorities, CPS is currently focused on industry issues involving animal feeding operations and agricultural water, Dr. Whitaker says.
The Acheson Group works closely with food producers at every level of the supply chain and determines how risk that isn’t adequately controlled upstream in the supply chain can carry through to the consumer. “When working with companies that grow, harvest, and process leafy greens, we look at the areas of greatest risk relative to food safety using FSMA’s regulations as a guide,” says Peyman Fatemi, PhD, vice president, Scientific Affairs, The Acheson Group, Big Fork, Mont. “FSMA regulations, when fully implemented, will go a significant distance in developing programs that will prevent microbial contamination in leafy greens.”
The Acheson Group is also working to incorporate the most current science to guide its recommendations. “Prior to the romaine outbreaks of 2018, the industry had not been treating its overhead irrigation water, which was drawn directly from irrigation canals,” Dr. Fatemi says. “There are still simple and logical steps, such as understanding the use and management of nearby land, that the industry can use to minimize the contamination of leafy greens.”
“The key is to perform a hazard analysis and then develop preventive controls to manage those risks,” Dr. Whitaker concludes. “And when contamination is discovered, it is equally important to perform a root cause analysis to identify why the contamination occurred and how it can be prevented in the future.”