(AP) -- The Food and Drug Administration is working with the Centers for Disease Control and Prevention to determine the source of contaminated cantaloupe blamed for a multistate listeriosis outbreak.

Several Colorado grocery stores have removed cantaloupe from shelves, though there has been no official recall.

More than two dozen cases of the outbreak strain of have been reported in Colorado, Indiana, Nebraska, New Mexico, Oklahoma, Montana and Texas, and four people have died. Health officials say most consumed whole cantaloupes, likely marketed from Rocky Ford in Colorado.

Rocky Ford cantaloupes, named for a region along the old Santa Fe Trail about 130 miles southeast of Denver, are prized for their above-average sugar content.

Jensen Farms in Holly, Colo., is voluntarily recalling cantaloupe it shipped to Illinois, Wyoming, Tennessee, Utah, Texas, Colorado, Minnesota, Kansas, New Mexico, North Carolina, Missouri, Nebraska, Oklahoma, Arizona, New Jersey, New York and Pennsylvania between July 29 and Sept. 10.