Challenges of Preventing Leafy Green Outbreaks

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.