Salmonella commonly originates in the feces of birds and animals, and could be introduced at a multitude of stages in the manufacturing process.
Common symptoms are diarrhea, fever, dehydration, abdominal pain and vomiting.
The CDC recommends that people who are ill and have eaten peanut butter see their doctors for a diagnosis and call their local health departments. Symptoms usually develop 12 to 72 hours after infection, and the illness lasts four to seven days.
The bacteria sickens about 40,000 people a year in the U.S. and kills about 600.
To get a refund, consumers should send lids and their names and addresses to ConAgra Foods, P.O. Box 57078, Irvine, CA 92619-7078. For more information, call 866-344-6970.