E. coli outbreaks can be caused by contaminated irrigation water

Dear Doctor: It seems like every time we turn on the TV there’s another recall of romaine lettuce because of another outbreak of E. coli. What’s the deal? How dangerous is it if I get infected?

Dear Reader: You’re right — there seems to be no end in sight to the safety issues having to do with romaine lettuce and E. coli bacteria. It’s understandable that there would be occasional safety issues in a food supply chain as vast and complex as the one that serves the United States. When it comes to romaine lettuce, though, the ongoing issues seem to be in a category all their own.

Let’s start with E. coli, the bacteria that’s causing salad lovers so much trouble. The full name is Escherichia coli, and it comes in many different strains, which live in the intestines of humans and animals. Most strains are harmless and co-exist peaceably with their hosts. However, some strains produce something known as Shiga toxin, a particularly nasty pathogen. Once the “bad” E. coli strains are ingested and reach the large intestine, they multiply rapidly. They then bind to the intestinal lining, which is rich in tiny capillaries. That gives the Shiga toxin a pathway to the kidneys.

The inflammation resulting from the presence of Shiga toxin is believed to cause the initial symptoms, which begin with abdominal cramping that can become quite severe. The diarrhea that follows often becomes visibly bloody. Sometimes this is accompanied by vomiting or, less commonly, fever. The incubation period is anywhere from one to 10 days, but most people become ill within three to four days of infection. This occurs when someone ingests contaminated food or drink, and through the oral-fecal route. The illness lasts anywhere from a few days to close to two weeks. For most, E. coli infection is extremely unpleasant but not life-threatening. But for young children and the elderly, such an infection can be fatal. That’s because they are at increased risk of developing hemolytic uremic syndrome, a form of kidney failure.

As for why romaine lettuce appears to be susceptible to infection with E. coli, the reasons aren’t completely clear. One outbreak was thought to be caused by water that flowed through an irrigation canal believed to be contaminated by the bacterium. In some cases, infections have been traced back to livestock operations that border fields of romaine. Other points of potential infection are processing facilities, where romaine is washed and bagged. The lettuce industry has pledged mitigations to address each of these issues, particularly those having to do with contaminated irrigation water.

In the meantime, it’s vital to abide by the Food and Drug Administration’s directives to steer clear of romaine. It may be tempting to keep whatever you have in your fridge and simply wash it thoroughly. Unfortunately, that won’t work. E. coli can hide in microscopic crevices, and it’s impossible to get rid of it all. In fact, the CDC recommends that consumers thoroughly clean the place in the refrigerator where the contaminated food was stored.

For the latest updates regarding foodborne illnesses and contaminants, including the romaine recalls, visit www.fda.gov/food.

Eve Glazier, M.D., MBA, is an internist and associate professor of medicine at UCLA Health. Elizabeth Ko, M.D., is an internist and assistant professor of medicine at UCLA Health.