So far, the outbreak has affected New Jersey, Idaho, Pennsylvania, Connecticut, Washington, Missouri and Ohio.
No word on what caused it. The strain linked to chopped romain lettuce is a Shinga toxin-producing E. coli, which can cause severe stomach cramps, diarrhea and vomiting, the CDC said. If you have some of the lettuce, or aren't sure where yours comes from, throw it out.
If you have already purchased products containing chopped romaine lettuce, including bagged salads, salad mixes or prepared salads, throw them away.
New Jersey has the largest share of people infected, with six cases reported in the state.
The CDC also advises that all restaurants and retailers ask their suppliers about the source of their romaine lettuce and refrain from selling or servicing any that was grown in Yuma.
Preliminary information indicates 26 of 28 people interviewed reported consuming romaine lettuce in the week before their illness started.
The CDC says individuals in the U.S. who have a chopped romaine lettuce product, such as a salad mix containing the leaves, should not eat it and instead throw it away.
It can also be transmitted if a person who is carrying the bacteria doesn't wash their after using the bathroom and then processes or prepares food.
The New Jersey Department of Health said there are seven cases of E. coli reported in New Jersey.
Six people have been hospitalized, with one developing hemolytic uremic syndrome, a kidney condition. At this time, ill people have not reported having eaten whole heads or hearts of romaine. Ill people range in age from 12 to 84 years, with a median age of 29.
The U.S. Food and Drug Administration, and the U.S. Department of Agriculture's Food Safety and Inspection Service are investigating, but so far haven't linked a specific food, grocery store, or restaurant chain as the source.
Identifying a common source for E. coli infections is particularly challenging because individuals could potentially eat several meals spanning several places before experiencing symptoms and falling ill.