Consumers anywhere in the United States who have store-bought romaine from Southwest Arizona at home, including salads and salad mixes containing that lettuce, should throw it away immediately, federal health officials said — even if some had already been eaten with no ill effects.

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This post has been updated.

WASHINGTON — Public health officials are now telling consumers to avoid all types of romaine lettuce from southwest Arizona because of an E. coli outbreak linked to the vegetable that has spread to at least 16 states and sickened at least 60 people, including eight inmates at an Alaska prison.

The Centers for Disease Control and Prevention said Friday that new information about the illnesses in Alaska led them to expand a warning beyond chopped romaine to include any type of romaine lettuce, including whole heads and hearts of romaine.

Although the exact source hasn’t been identified, federal health officials have said information indicates that the contaminated lettuce was grown in the Yuma, Ariz., area. But consumers anywhere in the United States who have store-bought romaine at home, including in salads and salad mixes, should throw it away immediately if they don’t know its specific source, officials said — even if some had already been eaten with no ill effects.

Of the people who have been sickened, at least 31 have been hospitalized, including five who developed a type of potentially life-threatening kidney failure known as hemolytic uremic syndrome. No deaths have been reported.

No common grower, supplier, distributor or brand has yet been identified. Symptoms of infection include bad stomach cramps, diarrhea (often bloody) and vomiting. Occasionally, more serious complications can occur, including kidney failure.

Consumers anywhere in the United States who have store-bought romaine at home, including salads and salad mixes containing that lettuce, should throw it away immediately, federal health officials said — even if some had already been eaten with no ill effects.

Officials also said consumers should throw away any lettuce if they’re unsure what kind it is. Consumers also should not buy or eat romaine lettuce at a grocery store or restaurant unless they can confirm it is not from the Yuma area.

The number of cases of illness has grown in the last several days. On Tuesday, a 66-year-old woman in New Jersey, Louise Fraser, filed a lawsuit in federal court against Panera Bread after claiming she ate contaminated romaine lettuce there and then had to be hospitalized for two weeks. As of Wednesday, the CDC reported 53 people were infected with the outbreak strain.

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Among the hardest hit states are Pennsylvania, with 12 reported cases, and Idaho, with 10. The case count includes one of the infected Alaska inmates; the remaining seven cases there will be included when the CDC provides its next count update, which is expected next week.

Romaine lettuce is sometimes packed in the field and shipped directly to restaurants or grocery stores. Other times, it is taken to a central processing plant, where it is packed under different brands before being sent to retailers, according to Bill Marler, a Seattle-based personal injury attorney who focuses on food-borne illness litigation and is representing several people sickened in the outbreak, including Fraser.

The different ways that romaine lettuce is harvested could make identifying the specific origin of contamination more difficult, Marler said.

As of Wednesday, the hospitalization rate for this outbreak was about 58 percent, much higher than the 30 percent normally associated with infections involving E. coli O157: H7, according to a CDC update sent to clinicians on Thursday. Health officials are working to determine “why this strain is causing a higher percentage of hospitalizations,” the notice said.

State and local health officials are continuing to interview sick people to ask about the foods they ate and other exposures before they became ill.

Most E. coli are harmless and actually are an important part of a healthy human intestinal tract. But a small number, including the strain in this outbreak, produce a toxin called Shiga that can cause serious illness or death in people.

This strain has been responsible for many high-profile outbreaks. The bacteria live in the intestines of cows, pigs and other ruminants. Infections start when someone swallows a tiny amount of human or animal feces through a variety of ways, including contaminated food, consumption of unpasteurized (raw) milk, unclean water or contact with the feces of infected people.

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A previous version of this story said that the CDC advised consumers to throw out all lettuce.

The Washington Post’s Kristine Phillips contributed to this story.