Lawsuits have been filed, as the multistate outbreak of E. coli O157:H7 HUS infection linked to romaine lettuce from the Yuma, Arizona growing region has grown to include 98 sick.
The Yuma region provides most of the romaine sold in the US during the winter.
The reported strain of E. coli, which produces poisonous substances known as Shiga toxins, can cause severe abdominal cramps, bloody diarrhea and vomiting.
While most E. coli bacteria are not harmful, some produce toxins that can cause severe illness.
The CDC says no deaths attributed to the outbreak have been reported. NBC said this is the worst outbreak since 2006 when illnesses traced to spinach killed three and sickened more than 270 people. Additionally, "we'd like to emphasize that most of the illnesses in this outbreak are not linked to this particular farm", Harris said.
The FDA is looking at two dozen other farms as the source of the chopped romaine tied to illnesses.
USA authorities have identified one farm as the sole source of romaine lettuce that affected consumers in Alaska, but there is no common link to other cases other than that the product was grown in Yuma, Arizona.
Speaking at the news briefing, he stressed that other area farms could also be affected.
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We'll update this article with more information as it becomes available, but today's CDC update is a reminder: Stay away from romaine lettuce.
Health officials say people shouldn't eat romaine lettuce unless they know it's not from Yuma. Because the growing season in the Yuma region is at its end, the farm is not growing any lettuce at this time. "Most people reported eating a salad at a restaurant, and romaine lettuce was the only common ingredient identified among the salads eaten".
Attorney Brendan Flaherty, who is representing clients sickened in this outbreak, said, "Everyone should know the symptoms of an E. coli infection".
"When I look at a bag of lettuce and it says product of the United States of America, do I know it's from Yuma?"
While chopped romaine sold either alone or in mixed salads was originally thought to be the culprit, last week the warning was expanded to include all types of romaine - chopped, whole heads and hearts of romaine, organic and baby romaine, and any salads or mixed salads that contain romaine.
Write down what you ate in the week before you started to get sick. The area generally supplies all of the nation's romaine between November and March, with harvesting moving north to California at about this time of the year.
The outbreak first began in April.