A salmonella outbreak that sickened nearly 400 people in the United States has been conclusively linked to peanut butter, Minnesota health officials said Monday.

State health and agriculture officials said last week they had found salmonella bacteria in a 2.25-kilogram package of King Nut peanut butter at a nursing facility in Minnesota.

Over the weekend, health officials tested the bacteria and found a genetic match with the bacterial, Salmonella typhimurium, which sickened 399 across the country with about one in five requiring hospitalization. All the illnesses began between last Sept. 3 and Dec. 29, but most of the people became sick after Oct. 1.

Following the finding, Ohio-based distributor King Nut Companies said it was recalling two brands of peanut butter, which were made by Virginia-based Peanut Corporation of America. The peanut butter was not distributed for retail sale to consumers, King Nut said. But it was distributed to establishments, such as care facilities, hospitals, schools, universities and restaurants.

Officials at the U.S. Centers for Disease Control and Prevention said poultry, cheese and eggs are the most common source of this particular strain.

Every year, about 40,000 salmonella illnesses are reported in the U.S., and many more are never reported, according to the CDC. Health officials recommend frequent hand washing and careful food handling and preparation to prevent foodborne illnesses.

Last year, a strain of salmonella traced to peppers from Mexico sickened 1,400 people in the U.S, including at least four Canadians returning from trips to the country.

Another 79 people in the U.S. fell ill after handling dry pet food contaminated with salmonella in October and November of last year.

With files from the Associated Press