An E. coli outbreak possibly linked to tainted lettuce has sickened at least 19 people in Ohio, New York and Michigan, including students on three college campuses, prompting a recall throughout much of the country.

Freshway Foods of Sidney, Ohio, said it was recalling romaine lettuce sold under the Freshway and Imperial Sysco brands in 23 states and the District of Columbia because of a possible link to E. coli.

Twelve of those sickened were hospitalized, three of them with life-threatening symptoms, the Food and Drug Administration said. The federal Centers for Disease Control and Prevention said it was looking at 10 other cases probably linked to the outbreak.

College students at the University of Michigan in Ann Arbor, Ohio State in Columbus and Daemen College in Amherst, N.Y., are among those affected, according to local health departments in those states.

The FDA is focusing its investigation on lettuce grown in Arizona as a possible source for the outbreak, according to two people who have been briefed by the agency. Donna Rosenbaum, director of the food safety advocacy group Safe Tables Our Priority and one of those briefed, said the agency held a phone call with public health advocates Thursday.

Rosenbaum and other public health advocates have long been pushing for stronger food safety laws. The House passed a bill last year that would give the agency much more authority to police food production, but the Senate has not acted on it.

The New York state Public Health Laboratory in Albany discovered the contamination in a bag of Freshway Foods shredded romaine lettuce on Wednesday after local authorities had been investigating the outbreak for several weeks. The bag of lettuce came from a processing facility that was also linked to the illnesses, the FDA said. The agency would not disclose the name of that facility or its location but said an investigation was under way.

E. coli infection can cause mild diarrhea or more severe complications, including kidney damage. The three patients with life-threatening symptoms were diagnosed with hemolytic uremic syndrome, which can cause bleeding in the brain or kidneys.

It was not immediately clear why students on college campuses were sickened. Freshway Foods said the lettuce was sold to wholesalers, food service outlets, in-store salad bars and delis.

Susan Cerniglia, spokeswoman for the public health department in Washtenaw County, where the University of Michigan is located, said it doesn't appear that students who were sickened ate the contaminated food on campus. It is believed they may have been sickened at local restaurants, she said.

The Erie County, N.Y., health department issued an alert late last month, however, that linked at least one diagnosis of E. coli to a student who ate at a Daemen College dining facility.

The most common strain of E. coli found in U.S. patients is E. coli O157. The CDC said the strain linked to the lettuce, E. coli 0145, is more difficult to identify and may go unreported.

Freshway Foods said in a statement Thursday that the FDA informed the company about the positive test in New York on Wednesday afternoon. The statement said "an extensive FDA investigation" of Freshway Foods' facility in Sidney has not uncovered any contamination at the plant.

The recalled lettuce has a "best if used by" date of May 12 or earlier. The recall also affects "grab and go" salads sold at Kroger, Giant Eagle, Ingles Markets and Marsh grocery stores.

The lettuce was sold in Alabama, Connecticut, the District of Columbia, Florida, Georgia, Illinois, Indiana, Kansas, Kentucky, Maryland, Massachusetts, Michigan, Missouri, New Jersey, New York, North Carolina, Ohio, Pennsylvania, Rhode Island, South Carolina, Tennessee, Virginia, West Virginia and Wisconsin.