The US  Agriculture Department is threatening to close down three poultry processing facilities in California linked to a salmonella outbreak which left 278 people sick across the nation.

In a letter sent Monday to Foster Farms, the USDA said sanitary conditions at the facilities were so poor that they posed a "serious ongoing threat to public health." The company was notified Monday of the USDA's decision.

The USDA took samples of the meat in September and found that raw chicken processed by those facilities included strains of salmonella were linked to the outbreak. Until now, the company has not officially recalled any of its products although Kroger, the nation's largest grocery chain, said Tuesday it will be removing all chicken from the three Foster Farms plants off their shelves. Kroger runs Fred Meyer and QFC stores in the Pacific Northwest.

The USDA first issued a health alert Monday warning consumers to avoid raw chicken from the three facilities after they detected strains of Salmonella Heidelberg, a strain that has been linked to human illness.

The chicken in question can be identified in supermarkets with USDA marks of inspection P6137, P6137A or P7632.

As a precautionary measure against the risk of salmonella transmission, all poultry products should be cooked to an internal temperature of 165 to kill disease-carrying pathogens. It is also important to properly wash hands and cooking surfaces before and after cooking.

According to CDC, the most recent outbreak began two weeks ago and is ongoing. The majority of illnesses have been in California but people in 17 states have been infected, from Texas to Michigan to North Carolina. The USDA had originally said the outbreak was in 18 states.