Out of the 84 infected, 42 people have been hospitalized, including nine people who have developed a type of kidney failure called hemolytic uremic syndrome, which can be life-threatening. No deaths have been reported.
The CDC is advising consumers to not buy or eat romaine lettuce unless you can confirm it is not from the Yuma, Arizona, growing region.
This advice includes whole heads and hearts of romaine, chopped romaine, and salads and salad mixes containing romaine lettuce.
"If you do not know if the lettuce in a salad mix is romaine, do not eat it," the CDC warns.