Since 2006, at least 13 recall announcements involving 135 pet products (e.g., dry dog food and cat food, pet treats, raw diets, and pet supplements) have been issued because of Salmonella contamination. The September 2008 recall involved approximately 23,109 tons of dry pet foods, representing 105 brands.
During 2006 and 2007, the CDC, the Food and Drug Administration (FDA), and multiple state health departments investigated 70 cases of persons infected with a strain of Salmonella Schwarzengrund. As a result of their findings, Mars Petcare US announced voluntary recalls of selected sized bags of two brands of dry dog food, both manufactured by the company at its plant in Everson, Pennsylvania. The recall was based on microbiologic testing by FDA, which found unopened bags of the two brands contaminated with the outbreak strain. All operations at the plant ceased during July to November 2007 to allow for deep cleaning. Despite the recall, the outbreak was isolated from more patients during the following months, brining the total number of cases to 79.
After additional outbreak-linked illnesses were identified in 2008, the FDA conducted another investigation. In August 2008, the FDA found the outbreak strain of S. Schwarzengrund in multiple brands of finished product at the plant, prompting another recall of products by Mars Petcare US. On September 12, the company announced a nationwide voluntary recall of all dry dog and cat food products produced at the Everson plant from February 18 to July 29, 2008, when production again was suspended at the plant. In addition, Mars Petcare US has taken steps to ensure that recalled products are no longer on store shelves. On October 1, the company announced that the Everson plant would be closed permanently. The FDA investigation is continuing.
This outbreak is the first documented outbreak to associate human Salmonella infections with contaminated dry dog food and to trace human illness to a contaminated pet food plant. The original source of contamination and mechanisms for continued contamination in the Everson plant over a 3-year period are unknown. The absence of cases during January to March 2008 suggests that cleaning and disinfection of the plant might have had some effect. The FDA is working with Mars Petcare US to better understand this problem.
Dry pet food has a 1-year shelf life, and contaminated product might still be in the homes of purchasers and could produce illness. Although the last reported case in this outbreak was tested on September 18, 2008, additional cases might occur. State and local health departments that identify ill persons with the outbreak strain should query ill persons or their caregivers to find out about pet-related exposures, including brands of dry pet food used in the home. When possible, pet stool specimens and samples of dry pet food should be collected and submitted for laboratory testing.