It was just a week ago that the Centers for Disease Control and Prevention issued a warning that probably messed up a few Thanksgivings across the country. An E. coli scare forced the CDC to tell everyone to throw out all romaine lettuce no matter what store it came from or where it was grown.

With very little information about the outbreak to draw from, health officials decided to issue a blanket warning against all consumption of romaine lettuce. Now, with a week of further investigation under its belt, the CDC is narrowing the potential sources of the E. coli contamination and has apparently traced it to growing regions in California.

“Based on new information, CDC is narrowing its warning to consumers,” the CDC writes in its latest update to the outbreak alert page. “CDC is advising that U.S. consumers not eat and retailers and restaurants not serve or sell any romaine lettuce harvested from the Central Coastal growing regions of northern and central California. If you do not know where the romaine is from, do not eat it.”

That’s a bit more optimistic than “don’t eat any romaine lettuce,” but the situation is a bit more complicated than it might sound. It’s often very difficult to know where store-bought lettuce was grown and, in this case, knowing its exact origins with utter certainty is of utmost importance.

The CDC says that any bags or labels indicating that the veggie was grown in the Central Coast region in central and northern California should be avoided. In some cases, lettuce products are mixed, as is the case with many premixed salads and chopped, bagged lettuce.

If you can’t be absolutely certain that the produce wasn’t grown in the affected areas, it’s best to completely avoid it for the time being. Health officials are still investigating the source of the outbreak and will hopefully know more sooner rather than later.

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