ATLANTA — An outbreak of E. coli linked to romaine lettuce grown in the Salinas region of California has spread to 23 states, according to the Food and Drug Administration (F.D.A.).

Health officials traced the outbreak to three farms in the region but are still investigating the exact source. A total of 102 illnesses and 58 hospitalizations have been reported, according to the Centers for Disease Control and Prevention. The cases are concentrated in Wisconsin, where 31 illnesses have been reported. Other states with cases include Arizona, California, Colorado, Florida, Iowa, Idaho, Illinois, New Jersey, North Carolina, Michigan, Minnesota, Montana, Nebraska, Pennsylvania, South Dakota, Texas, Virginia and Washington.

“This remains an evolving and fluid situation,” the F.D.A. said. “Information about our findings will be forthcoming as the investigation proceeds.”

The agency still advises restaurants, retailers, suppliers and distributors to voluntarily withdraw product grown in the region and withhold distribution of Salinas romaine for the remainder of the growing season. The region, which includes Santa Cruz, Santa Clara, San Benito and Monterey counties, produces 61% of the nation’s leaf lettuce. Romaine harvested outside of Salinas is not currently implicated in the outbreak investigation.