Although consumers should wash their produce before consumption, growers should not assume consumers will act as a final food safety checkpoint.

The incidence rate of foodborne outbreak recalls that implicate greenhouse-grown produce is statistically lower than that of field production, but greenhouses are not exempt, and the food safety issues of an outbreak are just as significant no matter where the produce is grown. Take, for example:

  • The 261 infected persons from 24 states — including 94 who were hospitalized and three who died — in a 2012 outbreak, in which a greenhouse well was listed as potentially contributing to Salmonella contamination and proliferation on cantaloupes.  The 84 people in 14 states infected in the 2013 greenhouse-grown Salmonella-contaminated cucumber outbreak. 
  • The more recent 5,000 cases of leafy greens recalled by a Virginia greenhouse in May 2017.
  • Greenhouse growers sometimes have a false sense of security around food safety issues, says Benjamin Chapman, North Carolina State University associate professor and food safety specialist. “The infrastructure gives the sense that they’re working in a protected environment, and there is a sense that it is very clean because it is not exposed to the environment.” However, not only are there openings through which birds and animals could enter, Chapman says, but hands, feet and water can all cause food safety risk.

    Chapman is a co-author of the manual, On-Farm Food Safety Guidelines for Greenhouse Vegetables. Although some of the science has changed since its 1998 publication so that “the things we now know may have filled in some of the science,” he says, the tenets of the manual, including many of those discussed herein, continue to provide a viable guide for greenhouse production. (The manual is available here)

    Birds and animals can squeeze into structures through very small openings — and doors that are not promptly shut. And once inside, they can easily contaminate produce. In fact, birds can be an even greater risk in greenhouses than in the open field, as they can nest over the plants in greenhouses and contaminate them with their droppings. In the field, there is no infrastructure on which to build nests. “So, it is a risk that isn’t outside,” he says.

    The importance of worker hygiene

    Personal hygiene and handwashing are significant aspects of risk management no matter where produce is grown. It was in the early 2000s that the industry began to focus on fresh vegetables and viruses, Chapman says. These viruses, such as Hepatitis A and norovirus, can be passed by ill workers not washing their hands before working with food. This is exacerbated by the condition of produce looking so clean at retail that consumers often don’t do anything to the fruit or vegetables before eating it — essentially treating it as a ready-to-eat food.

    As such, greenhouses should ensure they reduce barehand contact with produce and/or have a very robust hand sanitizing program, he says. Although consumers should be washing most produce prior to eating it, growers must not rely on them as a final food safety checkpoint. “We don’t want consumers to be the last CCP,” he says, in reference to the hazard control strategies of a Hazard Analysis and Critical Control Point (HACCP) program.

    The movement of pathogens into the greenhouse environment can come through walkways, cart rails, ladders, and any other way that foot or wheeled traffic is moving from the exterior to the interior. While many greenhouses do incorporate footbaths at entrances, “it takes the correct management of the footbath and use by employees,” Chapman says. “People may hop over it, or there may be no one checking the concentration levels.” Additionally, he says, if a footbath is in direct sunlight, it can change the efficacy of the composition.

    A look at water

    Water safety is a complicated issue no matter where one is growing produce, as evidenced by the complexity of requirements of the Produce Safety Rule of the Food Modernization Act (FSMA) — and FDA’s recent announcement that it is exploring ways to simplify the rule’s agricultural water microbial quality and testing requirements. While irrigation water is a major concern for field production, it is generally low-risk in greenhouses because, for the most part, it is targeted at the roots, so doesn’t touch the edible parts of the plant, Chapman says.

    However, the recent increase in the sale of rooted plants to consumers also increases the risk potential — as there is a risk of cross contamination from the roots to the edible parts of the plant, begging the question of whether roots should be treated with the same care as raw chicken — guarding against the risk of contamination to the “ready-to-eat” parts of the plant.

    Adding to the complexity is that fact that there is not much data on pathogens in irrigation water, Chapman says. While many greenhouses use only municipal water, some use runoff water, ponds or wells, so the safety of that water needs to be ensured. Wash-water tanks also can be a source of pathogens if the water is not managed correctly and chlorinated regularly to keep it free of contamination, he says.

    Other points to consider: processing and contact surfaces

    Another area that can be of concern, both for risk management and regulatory compliance, is greenhouses having an understanding of “minimally processed.” For example, if a greenhouse is doing any secondary cutting, slicing, dicing or shredding of the produce for packaging, the produce is now considered to be minimally processed, making the greenhouse subject to FSMA’s Preventive Controls rule.

    Additionally, the vast variation in greenhouse operations — both in size and geography, contribute to varying risk. For example, many large greenhouse operations have packing lines that look the same as those of large field growers, he says, so these food contact surfaces become a key factor for consideration in risk management. In the 2011 Listeria outbreak at Jensen Farms, multiple samples were pulled from the packing lines, which ultimately showed these food contact surfaces to be a factor in the outbreak. “It is analogous to what I see in greenhouses: people and lots of contact surfaces,” Chapman says. So, it is critical that these operations consider how to best keep those lines — and employee hands — clean and sanitized.

    “To be able to focus risk management steps, you need to be able to be in context with your entire operation,” Chapman says. “The false sense of security around GAPs starts to erode when an incident in the same type of facility you have leads to 84 illnesses.”

    Lisa is the editor of sister publication Quality Assurance & Food Safety (QA) magazine.