“I always wash lettuce to remove germs. That works, right?”–don’t bet your life on it! – Part 1: on the farm

Lettuce, like most leafy greens, presents a special food safety challenge.

Why? Because we eat it raw, and we place nearly all of our trust in what everyone else does before we purchase the lettuce–what they do on the farm, when harvesting, packaging, transporting, and storing the lettuce.

Unfortunately, we usually only learn what goes wrong when outbreaks occur.

Early days of produce food safety

It all started with raspberries in the 1990s, when more than 100 Floridians, including persons dining at posh Palm Beach restaurants, were infected by a parasite called Cyclospora. For most of the unlucky diners, it meant a protracted battle with diarrhea. But for some, those suffering immuno-compromising disease such as AIDS, it could mean death.

But who was the culprit? — Workers in Guatemalan raspberry fields, without adequate access to toilets and hand-washing facilities.

Here’s one scenario–a mother is picking raspberries with a child on her back. She needs to use the bathroom or the baby needs its cloth diaper changed. But there are no hand-washing stations in the field. As a result, her hands become contaminated with Cyclospora, which then contaminate the raspberries she’s picking.

Didn’t the raspberry company wash the raspberries, you ask? No, because raspberries are very delicate and washing shortens their shelf-life to such an extent that they would have spoiled before making the long trip to the USA.

Produce food safety today

We learned a lot from those outbreaks and from the unfortunate persons who suffered from Cyclospora. New regulations were implemented that now do not allow babies to be in the fields and that hand-washing stations must be located in convenient places for all workers.

Yet as we know, food safety problems continued after Cyclospora, especially those linked to leafy greens (like lettuce) contaminated with E. coli, Salmonella, and Listeria–three leading pathogenic bacteria.

In response, food companies have implemented even more safety measures before lettuce goes into a package–1) testing irrigation water, 2) not picking any lettuce within close proximity to a bird dropping in the field, and 3) dipping some types of produce in sanitizers.

But even with all of these protective measures, people still become ill.

Let’s say we own a lettuce farm and we test 1 gallon of irrigation water for Salmonella. The results come back negative (no Salmonella detected). Are we 100% assured there is no Salmonella in the thousands of gallons that we use to irrigate our lettuce field? NO. Our level of trust will be less than 100% because we only tested a small portion of the irrigation water. For example, if Salmonella was present in the water at 1 Salmonella cell per 100 gallons, then we would not detect it if we tested just 1 gallon. “Just test more water!” you might say. However, are you be willing to pay $20 or more for a head of lettuce, to support the cost of extensive testing? Probably not. Instead, we can have greater assurance about lettuce safety if we implement a whole series of food safety practices, such as using irrigation water that comes from a safe source, routine handwashing, and keeping animals out of the fields.

In Part 2, I discuss what we can do at the food store to enhance lettuce food safety.

If you wish, please share your comments about this blog.

4 Responses to ““I always wash lettuce to remove germs. That works, right?”–don’t bet your life on it! – Part 1: on the farm”

  1. Joe says:

    Do pathogens growth on lettuce?

    • foodsafety says:

      Good question.
      Most pathogens do not grow at refrigerator temperatures, with the exception of Listeria species. This species grows slowly, and if it reaches a sufficient level, it can cause illness in persons with pre-existing conditions (compromised health).
      However, nearly all pathogens will grow on lettuce if it is kept between 40 and 140F (Temperature Danger Zone), in which case the lettuce should not be eaten if left out for 4 or more hours.

  2. Sharon says:

    Should we wash triple washed produce? Also, what is the best method to wash salads and berries?

    • Mark says:

      Hi Sharon
      Assuming your question is about washing produce in a home setting, a single wash is typically all you need to do.Most bacteria, including pathogens, tightly adhere to the produce surface. The only way to ensure that there are no pathogens on the produce that you eat is to cook the produce or peel it (if relevant).

      As for washing produce, such as lettuce and berries, you can find information in Part 3 of this blog topic.

      If you need more information, don’t hesitate to contact me.

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