Another Romaine Warning? Microbiologist On Why Leafy Greens Are Vulnerable To E. Coli03:42
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Romaine lettuce is seen on sale at a supermarket in Washington, D.C., on Nov. 20, 2018. (Andrew Caballero-Reynolds/AFP/Getty Images)
Romaine lettuce is seen on sale at a supermarket in Washington, D.C., on Nov. 20, 2018. (Andrew Caballero-Reynolds/AFP/Getty Images)
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The Centers for Disease Control and Prevention warned Tuesday that all types and brands of romaine lettuce are currently unsafe to eat, as they may be contaminated with E. coli. This latest outbreak has many consumers wondering: Why are leafy greens so often the culprit when it comes to E. coli contamination?

Here & Now's Peter O'Dowd talks with Rachel Noble, an environmental molecular microbiologist who recently developed a test for identifying E. coli in produce water.

Interview Highlights

On why it’s difficult to find the source of the outbreak

"If you think about lettuce in particular, it's grown with an immense amount of water. They are water-loving plants. In addition to that, a lot of times, the areas in which they're grown, the water resources are coming in from canals or irrigation systems that are carrying water some distance. Furthermore, I think one of the things that people can think about from the perspective of lettuce is that we know whenever it's in our own gardens that it can have dirt and sand or sediment on it. And so the washing process is something for CDC to be looking at in terms of sources of this contamination."

"The most recent salad that you ate, you may not have washed it well enough to remove a lot of the sediment and sand and dirt, and that's really where the bacteria can be found."

Rachel Noble

On why lettuce is responsible for many E. coli outbreaks

"I really point to a few key reasons why lettuce. The first is that, even if people are using it … in a smoothie or in a juice drink, the product is still raw. So there are very few cases where romaine in particular is going to be cooked in any form. The second is that as I said these are plants that really love water and so an immense amount of water is used to grow them. And the third really is, if you think about it, there's a lot of nooks and crannies in romaine lettuce. The most recent salad that you ate, you may not have washed it well enough to remove a lot of the sediment and sand and dirt, and that's really where the bacteria can be found."

On how this kind of breakdown in food safety happens

"I think one of the reasons is … that it's impossible for us to test every single product with the current framework. We do a very good job in this country of tracking back to outbreaks. But one of the things that we don't do is, we don't do a lot of proactive testing because E. coli can come from a lot of different places. And so there's two real needs. One is that you need to measure the E. coli out in the environment, but then in addition to that, there's only a small subset of that type of E. coli that causes the disease that we're so concerned about. Most strains of E. coli are actually harmless. So we have this conundrum where it's not always true that lettuce that has a high amount of E. coli on it, it's not necessarily true that actually contains ones that can make you sick. And that's a conundrum because the two are not always related."


Savannah Maher produced and edited this interview for broadcast. Francesca Paris adapted it for the web.  

This segment aired on November 21, 2018.

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Peter O'Dowd Twitter Senior Editor, Here & Now
Peter O’Dowd has a hand in most parts of Here & Now — producing and overseeing segments, reporting stories and occasionally filling in as host. He came to Boston from KJZZ in Phoenix.

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