Five Myths About Food Safety and Home Gardens

As both a medical school professor and someone with experience growing (and even engineering) microorganisms, I’m not naïve about the potential for foodborne illness from my home garden. That said, I still consider the produce that I consume from my tiny plot to be far less risky than anything I might pick up at a grocery store or restaurant.

And this week’s report from the CDC provided further evidence that my home garden is the safest source of food for my family. This report examines the links between food commodities and foodborne illness, identifying fresh produce as the most frequent offender… a whopping 46% of all cases! For historical perspective, fresh produce was linked to less than 1% of all foodborne illness in the 1970s, and less than 12% in the 1990s. Why is foodborne illness from produce on the rise?

Although some of the observed increase in produce-linked illness could be due to improved source identification methods, a good bit of it is due to changes in how we consume our food. Almost half of foodborne illnesses linked to fresh produce were caused by infection with noroviruses, which infect cells lining the gastrointestinal tract, producing diarrhea and vomiting. In the majority of these outbreaks,investigators were able to trace contamination to a single infected food handler who was contaminating raw or lightly cooked foods, such as salads or sandwiches. So, much of the rise in illness linked to produce results from the U.S. becoming a Fast Food Nation since the 1970s – we consume convenient foods with the risk of inconvenient illness.

Can you just prepare your foods at home if you want to avoid being the one out of every six Americansthat will get a foodborne illness this year? Not quite. There are many human pathogens showing up in our store produce aisles now, including Escherichia coli and Salmonella species, once only associated with uncooked beef and poultry. In contrast to norovirus, these pathogens are far more deadly. They are also contaminating our food as it grows in the field, during harvest, as it washed and packaged, or as it is distributed… anywhere along the food chain. When produce is centralized in large industrialized farms or packaging facilities, contamination can easily spread and be distributed widely. The decline of small farms in America is real, and we have heard of too many examples of agricultural operations with unsanitary practices, the result of no longer having to look the consumer in the eye when their produce is sold.

With so many players involved in the production and distribution of our country’s food, accountability for safety is difficult. Until recently, the Food Safety and Modernization Act, signed into law by President Obama in 2011, did little to address the risk of foodborne illness from produce. That changed in early 2013 with the proposal of a new FSMA rule focused on standards for produce safety. Although these standards should help reduce the incidence of foodborne disease, they will not be enacted until an 18-month review and public comment period has been completed.

What’s a reasonable person to do in the meantime? Get to know your food. Buy at reputable farmers’ markets, ask questions, and get to know the wonderful people who are growing your food. Even better, grow your own.

foodborne illness from your garden?

Growing your own food is one step towards food safety, but there are published examples of families sickened by food that they have grown themselves (although rare). If you are to effectively reduce the risk of foodborne illness from your garden, you must also take some time to learn how human pathogens can gain access to your backyard, how simple management practices can reduce the risk of contaminating produce, and how to properly clean and store fruits and vegetables. You don’t need a Ph.D. to understand them, but I’m happy to provide you with a start by addressing five common myths about produce safety.

myth 1: washing or peeling produce is sufficient to remove pathogens.

If we’ve learned anything from all of these produce outbreaks, it is that prevention of microbial contamination is the most important food safety element. That is because many human pathogens bind food surfaces quickly and, in most cases, irreversibly (in some cases within 30 seconds). Once bound, many bacteria are capable of producing substances called biofilms that allow them to survive, grow on the surfaces of fruits and vegetables, and even withstand chlorinated water baths. These sticky biofilms are resistant to cleaning, even with soap or those vegetable washes sold in stores (which experts say you SHOULDN’T use, by the way, as they can be absorbed and affect flavor).

We are also learning that many human pathogens can invade the internal parts of plants, gaining access to interior plant tissues through injured roots or stomata (the leaf pores which allow plants to exchange oxygen and carbon dioxide with the environment). Motile bacteria, such as Escherichia coli and Salmonella, are especially good at this, and can even trick the cells guarding these pores to open.  Once a pathogen is internalized in this manner, washing is completely ineffective.

The way in which you wash your produce may even put you at greater risk of contracting a foodborne illness. Take a sun-warmed tomato from your garden and plunge it under cold running water, and the gases within the tomato tissues contract, creating hydrostatic pressure that pulls in microorganisms. Improper wash-water temperatures have been responsible for numerous outbreaks, including Salmonella in mangoes and tomatoes. Experts recommend that rinse water be as close to the temperature of produce as possible (within 10 degrees Fahrenheit).

And peeling to remove microbial contaminants? Recall that many pathogens can move into plants and infect internal tissues. But even if internalization of a pathogen hasn’t occurred, microbes can easily be transferred from knives to the tissue beneath a peel. Once there, damaged plant tissues release nutrients on which microorganisms can feed to support growth. It is therefore best to wait and peel fruits and vegetables until you are ready to consume them, or immediately refrigerate them. And of course, keep your hands, your kitchen, and your cutting tools clean to avoid cross-contamination.

myth 2: organic produce is more likely to cause foodborne illness. 

You don’t have to garden organically, but many people are choosing to do so. Although there are a limited number of studies that have compared conventional and organic produce, the consensus is that there is no difference between the two in the number or types of human pathogens. Only one study ever noted a greater percentage of E. coli on vegetable samples from organic farms, which the authors attributed to the sampling method (biased for sampling leafy greens, which comprised about 33% of all samples from organic farms, and only 5% from conventional), concluding it was produce type rather than farm type that influenced contamination potential. Further, few studies have distinguished between certified organic and non-certified organic farms. In the one study that did distinguish by farm type, not a single produce sample from certified organic farms contained E. coli, whereas non-certified organic and conventional farms did (as high as 25% of leafy greens from conventional farms, and 30.8% of lettuce from non-certified organic farms).

Why do so many people believe that organic foods are more likely to harbor pathogens than conventional, when the evidence speaks otherwise? Primarily because of public misconceptions about manure use in organic and conventional agriculture. Both conventional and organic practices use manure as fertilizer, but they differ in how manure use is managed.

Manure use on certified organic farms is strictly regulated. The National Organic Program (NOP) specifies that if manure is not composted, it must be tilled into the soil at least 120 days before the harvest of a food crop that comes in contact with soil (like leafy greens), or at least 90 days before the harvest of a crop that does not come into contact with the soil (like corn). Certified organic farms must pay certification fees, keep records, and are subject to inspection to insure that they comply with these standards.

What are the rules for manure use in non-certified organic or conventional farms? With regards to ensuring food safety, none. Although many states mandate that farmers have a Nutrient Management Plan (to prevent nutrient runoff and subsequent pollution of streams), there are currently no restrictions on timing of raw manure applications for conventional farms. In fact, many conventional farmers lease their land to factory farms for manure disposal. Concentrated animal farm operations (CAFOs) produce well over 1 billion tons of manure each year – it has to go somewhere, and many conventional farms gladly allow the raw manure to be spread on their fields, both for the free fertilizer and the additional money.

If you are going to use manure in your garden, use it safely. Proper composting kills pathogens shed into animal manure, but most home compost systems cannot reach the high temperatures (at least 131 degrees Fahrenheit) required to kill them; commercial composted manure may be the safer choice. If you must use raw manure, follow certified organic methods and till the manure into your soil well in advance of planting as discussed above. You should know that among the rare cases of illness linked to home gardens, they resulted from exposure to freshly-spread raw manure, most commonly in young children, so make sure that your garden helpers wash their hands.

myth 3: bacteria like e. coli and salmonella are killed by pesticides.

Some folks mistakenly believe that conventionally-grown foods, since they are sprayed with pesticides, are purged of microorganisms that can cause illness. There are two errors with this line of reasoning. First, organic produce may also be sprayed with pesticides, albeit natural rather than synthetic formulations, so organic doesn’t mean pesticide-free. Second, although there are some broad-spectrum pesticides that kill many types of organisms, most have modes of action that are specific against certain types of pests, such as bacteria, fungi or insects. So, a pesticide may kill bacteria, but many certainly do not.

We’ve also come to understand that spraying pesticides can actually cause microbial contamination. How so? Farmers frequently mix and dilute pesticides in non-potable water that contains microorganisms, which are then sprayed directly onto plant surfaces. What’s worse is that some of these pesticide formulations actually support the growth of bacteria in the pesticide holding tanks, so if a farmer doesn’t use an entire tank in an application and allows it to stand until the next, the microorganism population grows sufficiently larger. This has been the source of contamination in many outbreaks, so much so that it is a problem targeted by the FSMA in the proposed produce safety standards.

If you do choose to use pesticides in your home garden, organic or conventional, make sure that you are using a microbe-free water source, such as water from your municipal supply. If you use well water, make sure that is tested for pathogens (which is a good idea anyway). Mix only the amount of pesticide that you need for a single application.

myth 4: i don’t apply manure to my garden or have pets, so i don’t have to worry about pathogens causing foodborne illness.

Can you control every bird, mouse, or insect that enters your garden? Any of these organisms could potentially vector pathogenic microorganisms. And not all human pathogens must use other animals as hosts. There are many pathogenic organisms that are native to soils, including Listeria monocytogenes(responsible for this past summer’s cantaloupe outbreak) and Clostridium botulinum (producing the fatally-ingested botulin toxin).

Do you use a rain barrel or water your garden from a nearby garden or creek? Just because you can’t see something growing in it doesn’t mean there isn’t anything there. These water sources can still be used safely in the garden – just use them for drip irrigation rather than spraying from above (which is more water-efficient to boot).

And if you use compost teas and/or manure teas, please remember that these can potentially harbor human pathogens. Brew teas with potable water. Use commercial compost, or buy dried manure from a reputable source that regular tests for pathogens (such as Authentic Haven Brand teas).

myth 5: since i am growing my own food, i don’t need to wash or refrigerate it after harvesting.

There are certainly many foods from your garden that you don’t want to refrigerate, such as tomatoes or potatoes, as doing so would negatively affect their flavor or appearance. And washing some produce, such as berries, significantly shortens their shelf life in the refrigerator – don’t wash them until immediately before you consume them. Other than these exceptions, most foods are not only safer if they are washed, dried, and stored in the refrigerator, but their flavor is preserved as well.

Why is it important to properly cool vegetables, wash them, and dry them well before storing in your refrigerator? Unlike most human pathogens, soil-inhabiting Listeria can grow in the cold temperatures of a refrigerator, especially under moist conditions (albeit more slowly than on your countertop). For produce that contacts the ground as it grows, such as cantaloupes and muskmelons, allow them to cool completely, wash under cool water with a vegetable brush (to remove dirt stuck in their netted skins), and dry completely.

a final word…

Don’t be scared, just be aware. When working in your garden, harvesting vegetables, or preparing meals, think about how you can minimize your risk of foodborne illness. And remember, the best way to know what is in your food is to grow it yourself. So, get growing!

Cathy is the author of Mother of A Hubbard.  She is also a medical professor, mother of two, and a gluten free cook.

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