Our in-house Know-It-Alls answer questions about your interactions with technology.

Q: Did the CDC really just ban… romaine lettuce?

A: The Centers for Disease Control and Prevention didn’t ban lettuce or recall it—it doesn’t have the regulatory power to do either of those things—but two days before Thanksgiving, it put out an unusually strong statement telling Americans to toss any romaine lettuce in any form: whole, chopped, pre-bagged into Caesar salads, combined into spring mix, and so on. The warning covered not just homes but retailers and restaurants, and came with a recommendation to empty any fridge where romaine has been stored, and wash it out with soap and warm water.

The CDC said it was making the recommendation to not eat, serve or sell any romaine lettuce because 32 people in 11 states, plus 18 people in Ontario and Quebec, have been made ill by E. coli O157:H7, which causes very serious illness because it produces a toxin that destroys cells lining the intestines and kidneys. The patients are all infected with the same strain, based on genetic fingerprinting, and the only thing they have in common is that they all ate romaine.

But, the CDC said, “no common grower, supplier, distributor, or brand of romaine lettuce has been identified.” The agency isn’t usually so sweeping in its statements, but with a holiday coming—one that’s centered around eating and that takes people offline into the real world of airports and cars and dinner tables—it warned against all romaine until the threat can be better defined.

The Food and Drug Administration, which does have the power to compel foods to be recalled, is investigating, along with health departments in the 11 states where people have gotten sick.

Wasn’t there a romaine problem just recently?

A couple of them—which suggests there’s an ongoing problem, though no one has proved where the shared vulnerability is. A massive outbreak of E. coli O157 illness linked to romaine between March and June of this year sickened 210 people in 36 states, killing five of them; eight Canadians got sick as well, but survived. A separate O157 outbreak in 2017, caused by romaine in Canada and unspecified “leafy greens” in the U.S., sickened 42 Canadians and caused one death. Twenty-five Americans got sick too, one of whom died.

Going further back, wholesale salad mixes caused an O157 outbreak in 2013 (33 victims), a different brand of bagged salad caused a similar outbreak in 2012 (33 victims that time, too), and bagged spinach sickened 199 people in 26 states in 2006 and killed two elderly women and a baby.

The CDC said Tuesday that the E. coli strain in the current outbreak has the same genetic fingerprint as the 2017 outbreaks—but not the same as the giant romaine outbreak that occurred earlier this year.

Didn’t Arizona have something to do with this?

The outbreak earlier this year—the one that the CDC says was caused by a different strain—was traced back to Yuma, Arizona, which happens to be the place that grows most of the salad eaten in the U.S. between December and March. Lettuce growing in Yuma is highly high-tech: The fields are leveled with lasers to make sure no irrigation water gets wasted and the tractors are routed by satellites. Plus, the state maintains a “Leafy Greens Marketing Agreement,” the only place other than California to have one, that audits growing practices that are supposed to protect food safety.

None of that prevented E. coli reaching the lettuce fields, which are tucked up against the California and Mexican borders and irrigated by water pumped out of the Colorado River. An FDA-CDC task force that issued a report in November said that it found the outbreak’s E. coli strain in three samples taken from an irrigation canal that brings water to the farms. The task force couldn’t explain how the pathogen got there, but food-safety advocates think they know: E. coli comes from the guts of animals, and on the other side of the canal, there’s a cattle feedlot that holds up to 100,000 cows at a time.