The increase resulted not from a large number of new cases but from improved surveillance by state health departments and the fact that laboratories completed analyzing samples, said Dr. David Acheson, associate commissioner for foods at the administration Wednesday.

    At least 48 of the victims have been hospitalized. The ages of the patients range from under one to 88 years old, and 47 percent of them are female with the most recent onset of illness on June 5.

    Food safety experts have linked the outbreak to tainted raw round, plum and Roma tomatoes and have not yet identified the source of contamination.

    They have repeatedly said the outbreak has not been linked to a single restaurant, grocery or retail chain.

    Most produce in the United States are not tracked from the farm -- and that has made the job of finding the source of the current outbreak more difficult.

    "We may not ultimately know the farm where these came from," Acheson said.

    But investigators are focusing on Mexico and central and southern Florida, which were the biggest suppliers of tomatoes at the time of the outbreak.

(Agencies)