The U.S. Department of Agriculture has issued a public health alert for raw chicken produced by Foster Farms after 278 people contracted salmonella over the past six months.

The USDA Food Safety and Inspection Service has tracked 278 illnesses across 18 states to a salmonella Heidelberg infection stemming from raw chicken produced in three Foster Farms facilities in California. Most of the illnesses occurred in California, Foster Farms’ primary market.

"The outbreak is continuing," the FSIS said in a press release.

The Associated Press reports that the salmonella outbreak began in March and that the USDA was first notified in July. While researchers had a difficult time finding the source of the outbreak, they eventually traced it to Foster Farms’ California facilities through epidemiologic, laboratory and traceback investigations.

Currently, the FSIS has not linked the salmonella outbreaks to any specific product or production timeframe. The organization did note, however, that affected Foster Farms facilities stamp products with the marks “P6137,” “P6137A” and “P7632.”

Foster Farms said it is working closely with the FSIS and CDC to eliminate any occurrences of salmonella Heidelberg at its facilities.

“When the incidence of illnesses linked to salmonella increased, we wanted to know why and have worked quickly to identify and implement additional controls,” Robert O’ Connor, Foster Farms’ food safety chief and head veterinarian, told NBC News. “It is also important to reassure the public that the FSIS process has not been affected by the recent government shutdown.”

The FSIS has not announced a recall, but has instead reminded consumers to heat chicken to a safe minimum internal temperature of 165 degrees before consuming and to always take precautions when dealing with raw poultry.