CDC: Don’t eat romaine lettuce. If you have any, throw it away.

The Centers for Disease Control and Prevention issued a stark warning Tuesday: Don’t eat any romaine lettuce in the United States. In fact, if you have any in your home, you should throw it away. Do this “even if some of it was eaten and no one has gotten sick,” the CDC warns. And if you had some in your fridge or in a drawer, the CDC recommends sanitizing the area. (Read the CDC’s full advisory here.)

The reason for the dire warning is an outbreak of a strain of E. coli linked to romaine lettuce. Thirty-two people in 11 states have been sickened by the Shiga toxin-producing E. coli O157:H7 strain, and 13 of them were hospitalized. Additionally, 18 people have been infected in Canada.

It’s a significant warning from the CDC to call out all romaine. Usually, the agency tries to issue warnings on specific brands or manufactures of food. This time, they still haven’t found the common grower, supplier, distributor, or brand of romaine lettuce that’s making people sick. So to try to prevent the outbreak from spreading, they’re taking the extreme measure of warning consumers against all of it.

Symptoms of an E. Coli infection typically appear three to four days after exposure, and can vary, but often include severe stomach cramps, diarrhea (often bloody), and vomiting. There have been no deaths so far.

The CDC does not know where, exactly, this outbreak originated. But they do know it is linked to eating romaine.

This is not the first outbreak of E. coli from romaine lettuce this year. An outbreak that lasted four months (March through June) sickened 210 people, and killed five. Ninety-six people were hospitalized, and the CDC was able to trace the outbreak back to a romaine producer in Yuma, Arizona.

How does lettuce become contaminated with bacteria? As Vox’s Julia Belluz explained earlier this year:

Instead of buying heads of lettuce that we wash and chop or rip up ourselves, over the past couple of decades, sales of precut and bagged greens have boomed. These mixed greens wind up in our fridges or at restaurants already washed and ready to toss in a salad bowl. But during processing, bacteria living among the leafy greens have a moist environment in which to flourish.

“When you bag and chop [salad], bacteria just gets amplified — and when you ship it across the country, the bacteria has a chance to grow in the bag,” Bill Marler, one of America’s leading food safety attorneys who is representing families affected by [the spring] outbreak, told Vox after the outbreak was first declared.

What’s more, it can be hard to track down an outbreak to a single source. “Different lettuces grown at different farms get mixed into bags that are distributed at supermarkets and restaurants all over the country, so food safety officials need to search for the common link among suppliers,” Belluz writes.

The CDC is imploring restaurants and retailers to “not serve or sell any romaine lettuce, including salads and salad mixes containing romaine.”

We should all play it safe: Don’t eat romaine lettuce. Your Thanksgiving meal will be fine without it.