Human illness caused by Salmonella Schwarzengrund was detected beginning in January, 2006. During the summer of 2007, a case control study implicated exposure to pet foods produced by a single production plant of Mars Petcare US. The plant produced 25 brands of dry pet food. Specific distribution data of the products was not available. The outbreak strain of Salmonella was found in an environmental sample collected at the plant, in unopened bags of dry dog food produced at the plant, and in fecal samples of dogs that ate the food. Despite a pet food recall in 2007, cases continued to be reported through October, 2008. The outbreak had persisted over a three year period, likely because of continued contamination in the pet food production facility and the long shelf life of the products. This outbreak was the first documented outbreak to associate human Salmonella infections with contaminated pet food and to trace human illness to a contaminated pet food plant and resulted in permanent closure of the production facility. The original source of the contamination was never determined. No illness was reported from pets.