A Chicago-based law firm has announced its plans to file a class action lawsuit against US poultry producer Pilgrim's Pride on allegations that the company's products caused deaths and serious illness from listeria. The lawsuit refers to an outbreak of listeria in the northeastern US that caused several deaths and over 40 cases of illness. Listeria bacteria was found in Pilgrim's Pride Wampler Foods plant in Franconia, Pennsylvania in October. Officials at the Centre for Disease Control and Prevention said that the plant was the "most likely source" of that particular outbreak although they have yet to definitively link any Wampler product to the outbreak.