Over the past four years, the tree fruit industry has been on a crash course in listeria control, thanks to the rollout of the Food Safety Modernization Act and a 2015 outbreak of the pathogen L. monocytogenes in caramel apples that brought new scrutiny to whole fresh apples.

Researchers now know a lot more about how listeria — a common bacteria in soil and decaying vegetation, which is to say on farms — gets into packing houses and production facilities and how it can best be controlled.

Experts from the Produce Marketing Association and United Fresh Produce Association shared the best strategies at an April workshop hosted by the Washington State Tree Fruit Association in Yakima with a focus on long-term plans for risk reduction.

Listeria can linger in cracks and crevices — even under dry conditions — for months, ready to bloom when production resumes. That means it’s critical to find these hiding hot spots, remove the bacteria and figure out how to prevent contamination in the future.

Packers certainly don’t want to find listeria, but speakers at the workshop stressed that actively looking for it and finding it mark the best course of action.

Trevor Suslow

Trevor Suslow

“It’s not a problem that you found it. It’s going to be there,” said Trevor Suslow, vice president for food safety at the Produce Marketing Association. “It’s how you respond to it that matters. Environmental monitoring programs must drive long-term change and improvements.”

In the short term, listeria control means more testing and more thorough training of sanitation teams. In the long term, packers should look to improved equipment and facility design to reduce risks and make sanitation more efficient.

“Cleaning and sanitation verification remains challenging,” Suslow said. A recent survey in California citrus packing facilities found listeria in routinely wet areas, including under anti-slip mats, cold curtains that collect condensation, floor drains, cull transfer belts and wall cracks caused by forklift damage, to name a few.

The specific regulations at play depend on what provision of the Food Safety Modernization Act a facility must follow; the Preventive Controls for Human Food rule requires environmental monitoring to verify sanitation, while the Produce Safety rule does not. Regardless of regulatory classification, packers must ensure their produce is not contaminated with L. monocytogenes (“L. mono” for short).

“Ultimately, it is your responsibility to produce food that is safe for consumption. That is the bottom line,” said Mickey Parish, senior science adviser for the FDA’s Center for Food Safety and Applied Nutrition.

Test but verify

Most packers test for generic listeria, so that if there is a positive test, it would prompt a corrective action without the produce being considered adulterated and triggering a recall.

The FDA supports this approach because it wants the producers of fresh produce to be looking for listeria and working aggressively to reduce it, rather than being afraid of what they might find, Parish said. This approach helped the meat industry drive listeria contamination down dramatically, he said.

However, while training workshops often focus on how and where to sample effectively, you cannot simply sample your way into safety, Suslow said.

There’s no one-size-fits-all environmental monitoring program, he said. It depends on facility size, the number of lines, known hot spots and the budget available. The goals are to prevent transient listeria from establishing, verify that control measures are working, catch hot spots before they can spread, and determine what corrective actions are necessary.

To keep testing costs down, Suslow recommended combining several swabs from similar areas into one sample for testing. Then if it tests positive, the exact location isn’t clear, but the mitigation can address the entire area sampled, such as one belt or equipment footings in one area.

Testing can take the form of molecular diagnosis or cultures, and the technologies for both are advancing. Suslow said the molecular tools are now very reliable. “If you get a molecular positive, believe it and act on it, don’t wait to culture it,” he said, adding that people tend to only want to double-check positive results with a culture, and that’s a mistake.

“If you didn’t trust the positive you got yesterday, why would you trust the negative you got today?”

Doing speciation may also not be necessary in the environmental monitoring plan, unless there is a specific, persistent problem that needs troubleshooting.

“It’s our opinion that if you should get positive for listeria species, presume you’ve got L. mono in there,” Suslow said.

As far as labs that offer whole genome sequencing, workshop speakers suggested that while the pathogen fingerprinting technique works well to help the FDA investigate outbreaks, it offers little use to most packers at this point and could add risks since the FDA could subpoena the data from packers, as part of future investigations, if warranted.

Design for better sanitation

For the most part, packing lines were not designed for the level of sanitation food safety programs now require. Hard-to-clean areas such as rough welds, laminations, cracked conveyor belts, hollow rollers, bold threads, electrical boxes and wrapped cords can all harbor listeria.

As manufacturers and facility designers start to respond to the risk, improved equipment is becoming available that is easier to clean and sanitize, said Alan Heinzen of Blue Sky Sanitary Design. All equipment needs to be cleanable — no aluminum — and the easier it is to clean, the more likely crews are going to do a good job cleaning and sanitizing.

New options include: building equipment with open-frame stainless steel instead of tube steel that could harbor pathogens; urethane coatings that seal concrete floors and equipment footings; sealed switch boxes; conveyor belts that lift up for ease of cleaning; and even etched part numbers of equipment rather than labels.

“It’s a function of how much money do you want to spend and how clean you want your plant to be. There’s a lot of compromises to be made,” he said.

Few facilities have the budget to make wholesale equipment changes for food safety purposes, but small changes can make big improvements for legacy equipment, said Melissa Ortner, a food safety consultant with Channelized Integrated Solutions.

“The vast majority of older stuff was not designed with sanitation in mind,” she said. “The last 10 years we’ve been on a great learning curve in sanitary design.”

It can be overwhelming at first to look at how many issues legacy equipment can pose, so Ortner recommended prioritizing by zone. In the food safety world: Zone 1 is food contact surfaces such as flumes, belts, sizers and employees’ hands; Zone 2 is near-contact surfaces such as the outside of equipment; Zone 3 includes floors and drains; and Zone 4 is parts of the facility outside the produce handling space, such as offices, locker rooms or loading docks.

Bringing a food safety mindset to a facility is a team effort, so work with cleaning, sanitation and maintenance staff to discuss how best to address problem areas, such as laminations in processing equipment, rough welds that can harbor bacteria, rusty drains or hollow rollers.

Ortner also recommended talking with manufacturers about how equipment could be improved and bringing in an outside perspective with fresh eyes who can help find risks that food safety program managers might miss in their own operations.

Making improvements comes at a cost, but in addition to lowering the risk of listeria contamination, making facilities easier to clean and sanitize reduces the cost and time of that work.

“It’s all about continual improvement. You don’t have to do it all at once,” Heinzen said. 

What about Zone 1?

Today, most packing lines swab for pathogens in Zones 2 and 3, not direct food contact surfaces. That’s because, historically, finding a positive on a food contact surface – even for generic listeria — necessitated withholding or recalling product from distribution.

In the new draft guidance on listeria control, the U.S. Food and Drug Administration said that it no longer requires treating an initial positive that way unless there is a recurring issue, but many in the industry remain wary of this risk.

The FDA hopes that change will encourage more testing and more response.

Mickey Parish

Mickey Parish

“We do recommend you do Zone 1 testing because we believe it is a benefit to help you track listeria,” said Mickey Parish, senior science advisor at the FDA. “But a lot of people still don’t use Zone 1 testing in their plans, and that’s OK because the guidance document is a recommendation. You don’t have to do it as long as you have the same results and show us that you have a robust control plan.”

Some customers now want to see Zone 1 testing, however.

In that case, United Fresh Produce Association’s Emily Griep recommends testing while the equipment runs empty, before operations, or doing a test run with a few bins that won’t be sold until test results come back. It’s also a good idea to build up a strong listeria control plan before moving to test Zone 1, she said.

If the FDA comes to inspect a facility in a for-cause situation, they will definitely test Zone 1, and everywhere else, in what food safety insiders call a “swabathon.” That means product should be held until the test results come back, Griep said.•

—by Kate Prengaman

Missed the workshop but want to learn more? Last year, United Fresh and the Washington State Tree Fruit Association prepared guidance on listeria control specifically for the tree fruit industry, which is free on the United Fresh website at unitedfresh.org/listeria-monocytogenes. It’s also available for WSTFA members on its website, along with other resources and video trainings at wstfa.org.