Investigators are zeroing in on romaine from California as the source of E. coli poisoning, and the lettuce trouble reveals why outbreaks are so common

  • The Centers for Disease Control and Prevention is investigating a multistate outbreak of E. coli that has sickened at least 65 people across the US and Canada.
  • Investigators are zeroing in on the romaine-growing region in central and northern California as the source of the outbreak. Romaine lettuce that was not grown in California has been deemed safe to eat.
  • This is the third time in less than 12 months that romaine lettuce has been deemed dangerous to eat.
  • The problem shows how difficult it can be to control a supply of fresh, uncooked produce that touches water and dirt, and changes hands countless times before it reaches consumers.
  • Still, fresh produce is not the deadliest source of pathogens that we eat. That prize goes to meat.

Salad eaters, rejoice: romaine lettuce is safe to eat again, as long as the leaves aren’t from California.

The Centers for Disease Control and Prevention (CDC) announced last week that it is investigating an E. coli outbreak that spans at least 12 US states and three Canadian provinces. So far, at least 65 people have gotten sick.

The CDC originally warned the public not to eat any romaine lettuce, just two days ahead of Thanksgiving. Simply “throw it away,” officials advised.

But investigators have now zeroed in on some end-of-season Californian lettuce from the state’s Central Coast growing region as the outbreak’s culprit.

“Romaine lettuce that was harvested outside of the Central Coast growing regions of northern and central California does not appear to be related to the current outbreak,” the US Food and Drug Administration (FDA) announced Monday. “Hydroponically- and greenhouse-grown romaine also does not appear to be related to the current outbreak.”

Since it can be tough for consumers to know exactly where their lettuce was grown, the FDA is also proposing some new voluntary romaine salad labeling guidelines. The FDA’s proposed labels would include information about where the lettuce was grown and when it was harvested.

The revision comes as romaine harvesting season winds down in central and northern California, and picks up in lettuce-growing states like Arizona and Florida, as well as Mexico.

Lettuce-related outbreaks are starting to feel like a wintertime tradition. Seven months ago, another E. coli outbreak in romaine from Arizona killed five people and sickened nearly 200 more. A year ago, one person was killed in another leafy-green outbreak that made 25 people ill. Here’s why this keeps happening.

There’s only one way that romaine gets contaminated with E. coli

E. coli is a broad species of gut bacteria (you have some of it in your intestines right now), but the strains that public-health investigators have discovered in sick people’s feces recently are not the kind that keep us healthy. Instead, the E. coli in question – called O157:H7 – can make people develop bloody diarrhea, stomach cramps, vomiting, and kidney failure. In severe cases, the gut poisoning can kill. It’s most dangerous for elderly adults and children.

An E. coli outbreak in lettuce can only mean one thing: The leaves have poop on them. The feces could come from livestock in a farm close to where lettuce grows, or they could come from washing or watering the lettuce in water that’s not clean. The contamination could also come from one of the countless people who touch the lettuce before it reaches consumers’ mouths.

Read More: What is E. coli?

It’s pretty easy for bits of contaminated soil or water to get lodged into the folds of lettuce leaves. Although washing your produce at home can help reduce the chances of infection, it won’t eliminate your risk of getting sick. That’s probably why fresh produce accounts for nearly half of all foodborne illnesses in the US.

An easy way to reduce your risk of getting sick, though, is to cut down on the number of hands that touch your leaves before you eat them.

Tim Richter, a romaine farmer in Puyallup, Washington, told the Associated Press that he encourages his customers to buy their own romaine heads and then wash and chop them at home, rather than buying pre-chopped bags of lettuce. That way, the leaves touch fewer hands, knives, and countertops as they go from soil to table. (Of course the cautionary step won’t help prevent infection if lettuce was already contaminated in the field.)

There’s probably nothing inherently bacteria-prone about romaine lettuce as compared to other fresh leafy greens. Outbreaks probably just affect more people and are easier to notice when tied to a leaf that’s commonly consumed. Lettuce is one of the most common veggies on American plates, and romaine’s share of the market has been growing steadily since it was introduced in the late ’80s. Romaine and leaf lettuce account for well over 60% of per capita lettuce consumption across the US, according to the USDA.

“I think that the issue isn’t that there’s more unsafe food,” FDA commissioner Scott Gottlieb said on the day the outbreak was announced. “I think what’s happening is that we have better technology than ever before to link outbreaks of human illness to a common pathogen.”

Uncooked leaves are not the deadliest thing on the menu

People infected with the O157:H7 strain of E. coli can develop “severe abdominal cramps and watery diarrhea, which may become bloody within 24 hours,” according to the Merck Manual.

“People usually have severe abdominal pain and diarrhea many times a day. They also often feel an urge to defecate but may not be able to,” the manual says. In severe cases, the illness can lead to kidney failure.

There’s typically no fever involved, and there isn’t much that otherwise healthy people can do about the infection besides staying hydrated. It can take anywhere from one to eight days for the illness to pass.

Fresh produce is the most common source of food contamination, but food poisoning from meat and poultry is more deadly.

Taken together, meat and poultry account for 29% of the foodborne illnesses that kill people, while produce (fruit and vegetables combined) accounts for 23% of deaths.

In fact, veggies are not even the worst source of E. coli infections – beef’s track record is equally bad. Vegetable row crops (mostly leafy greens) and beef each account for roughly 40% of E. coli cases across the country, according to a 2013 CDC report.

Chicken and other poultry can also get people really sick – the birds are commonly a source of listeria and salmonella infections. During Thanksgiving, a salmonella investigation was underway for raw turkey that sickened more than 160 people and killed at least one.

The good thing about meat is that correct preparation involves an easy “kill step” – cooking it to a high temperature ensures you won’t sick. But there isn’t a step like that for fresh greens. That’s why the CDC urges travelers not to eat fresh salad or unpeeled fruits in developing countries, where night soil (i.e. human manure) might be used as fertilizer, and water used to rinse fruits and veggies may not be clean enough to drink.

Fortunately, these contamination concerns are less of an issue in the US. Americans consume, on average, nearly 25 pounds of lettuce per person each year. So a couple dozen cases of food poisoning this fall (while miserable for those infected) are still a drop in the proverbial salad bowl.