Federal health investigators said Thursday they strongly suspect the culprits are Peter Pan peanut butter and certain batches of Wal-Mart's Great Value house brand both manufactured by ConAgra Foods Inc.

    Shoppers across the country were warned to throw out jars with a product code on the lid beginning with "2111," which denotes the plant where it was made. The suspect peanut butter was produced by ConAgra at its only peanut butter plant, in Sylvester, Ga., federal investigators said.

    "We think we have very strong evidence that this was the brand of peanut butter. Now it goes to the next step of going to the place where the peanut butter was made and focusing in on the testing," said Dr. Mike Lynch, an epidemiologist at the Centers for Disease Control and Prevention.

    It's the first time peanut butter has been suspected of causing salmonella in the United States. The only known salmonella outbreak in peanut butter occurred in Australia during the mid-1990s was blamed on unsanitary plant conditions.

    Peanuts are usually heated to high, germ-killing temperatures during the manufacturing process, so government and industry officials said the contamination may have been caused by dirty jars or equipment.

    "The heating process is sufficient to kill salmonella, should it be present," said Mike Doyle, director of the University of Georgia's Center for Food Safety, in the state that produces nearly half of the nation's peanuts.

    ConAgra said it is not clear how many jars are affected by the recall. But the plant is the sole producer of the nationally distributed Peter Pan brand, and the recall covers all peanut butter -- smooth and chunky -- alike produced by the plant from May 2006 until now.

    An estimated 974 million pounds of peanut butter are sold each year in the U.S. Peter Pan is one of the nation's top three brands, though well behind market leader Jif. Great Value peanut butter is also produced by some other manufacturers for Wal-Mart.

    "We're talking a lot of jars of peanut butter," said Dr. David Acheson, chief medical officer of the Food and Drug Administration's Center for Food Safety and Applied Nutrition.

    The highest number of cases were reported in New York, Pennsylvania, Virginia, Tennessee and Missouri. About 20 percent of all the ill were hospitalized, and there were no deaths, the CDC said.

    About 85 percent of the infected people said they ate peanut butter, and about a quarter of them ate it at least once a day, the CDC's Lynch said. It was the only food that most of the patients had all recently eaten.

    The outbreak was detected by the CDC and state health agencies when they noticed spikes in the cases of people sickened by an unusual type of salmonella, starting in August. Once peanut butter emerged as a link, the CDC notified the FDA.

    Other states reporting cases are Alaska, Alabama, Arkansas, Arizona, California, Colorado, Connecticut, Georgia, Iowa, Illinois, Indiana, Kansas, Kentucky, Massachusetts, Maryland, Maine, Michigan, Minnesota, Mississippi, Montana, North Carolina, Nebraska, New Jersey, New Mexico, Ohio, Oklahoma, Oregon, South Carolina, South Dakota, Texas, Vermont, Washington, Wisconsin and West Virginia.

    (Agencies)