November 26 (HealthDay News) -- A salmonella outbreak across dozens of states last year was caused by microwaveable frozen pot pies that weren't properly cooked, the U.S. government reported Wednesday.

And that highlights the need for safe preparation of such foods, according to the report, which will be published in the Nov. 26 issue of the Morbidity and Mortality Weekly Report from the U.S. Centers for Disease Control and Prevention (CDC).

The outbreak included 401 cases of salmonella infection (salmonellosis) in 41 states. Of the people who became ill, 32 percent were hospitalized. Investigators pinpointed Banquet brand frozen, not-ready-to-eat microwaveable pot pies as a source of the infections.

A further review determined that 77 percent of those sickened after eating the pies had cooked them in microwave ovens, and consumer confusion about microwaving instructions might have led to improper cooking of the pies. The manufacturer, ConAgra Foods Inc. of Omaha, Neb., issued a voluntary recall in October 2007 for all nine brands of pot pies, the report said.

Other microwaveable not-ready-to-eat foods, such as chicken nuggets and breaded pre-browned chicken breasts, have been linked with other salmonella outbreaks. Although some of these products appear to require only warming, they contain raw ingredients that require full cooking, the CDC report said.

Microwave ovens heat unevenly and that means some parts of a food item might be more thoroughly heated than other areas. To help prevent food-illness outbreaks, manufacturers need to provide clear labeling and cooking instructions on not-ready-to-eat foods so that consumers are aware of health risks and cook the foods properly, the CDC said.

SOURCE: U.S. Centers for Disease Control and Prevention, news release, Nov. 26, 2008