Tyson Foods is pulling nearly 8.5 million pounds of frozen chicken that could have been contaminated with listeria, the Department of Agriculture said.

The voluntary withdrawal was issued after Agriculture Department investigators were notified last month of two people who were sick with listeriosis, the department said in a statement Saturday.

An investigation found evidence linking those cases to frozen chicken from Tyson Foods, the agency said. Investigators eventually identified three cases related to the withdrawn products, including one death, the department said.

Symptoms of listeriosis, an infection caused by the bacterium Listeria monocytogenes, include fever, convulsions, muscle aches and gastrointestinal issues, according to the Department of Agriculture.

The products recalled were frozen, fully cooked chicken produced between December and April, the department said. Products include chicken strips, chicken pizza and pulled chicken breasts that were sold under brand names including Tyson, Jet’s Pizza and Casey’s General Store.

The packages have printed “placement code” P-7089, the department said.

In a statement, Tyson Foods said the recalled products were manufactured at a factory in Dexter, Mo. The company distributed the chicken to shops, hospitals, schools, restaurants and other places, the Department of Agriculture said.

“We are committed to providing safe and healthy food that people rely on every day,” said Scott Brooks, senior vice president for food safety and quality assurance at Tyson Foods. “We are taking this preliminary step out of an abundance of care and in line with our commitment to security.”

The Department of Agriculture said it would continue its investigation to determine if additional cases of listeriosis were related to the products withdrawn.

The department encouraged people to discard or return the remembered chicken. Pregnant women, adults over 65, and people with weakened immune systems are more susceptible to a serious case of listeriosis, according to the Centers for Disease Control and Prevention. Symptoms usually develop one to four weeks after eating food contaminated with listeria.