May 16, 2008 (CIDRAP News) – Contaminated dry dog food contributed to a Salmonella outbreak that sickened at least 70 people in 19 states in 2006 and 2007, many of them babies, the US Centers for Disease Control and Prevention (CDC) reported today.
An investigation of the outbreak—believed to be the first human Salmonella infections linked to dry pet food—was conducted by public health officials from Pennsylvania and other states, along with the US Food and Drug Administration (FDA). Findings appear in today's issue of Morbidity and Mortality Weekly Report (MMWR).
News of the outbreak came to light in June 2007 when PulseNet, an electronic network for sharing molecular data, identified Salmonella enterica serotype Schwarzengrund infections from a handful of states that had indistinguishable pulse-field gel electrophoresis patterns, according to MMWR.
Initial interviews of patients from Pennsylvania who were sickened by the outbreak strain suggested exposure to dogs or dry dog food; 8 (62%) owned one or more dogs, and the other 5 had regular contact with a dog.
Dog stool samples and dry dog food collected from some of the homes also tested positive for the same S Schwarzengrund strain. The two dog food samples that tested positive for the outbreak strain were both produced at the same plant in Pennsylvania, though there were two different brands.
The last reported illness onset date was October 2007. Most of the 70 confirmed cases were patients from Pennsylvania (29), New York (9), and Ohio (7). Of 61 patients for whom the age was known, 24 (39%) were age 1 or younger. Among 45 patients for whom hospitalization status was known, 11 (24%) were hospitalized, but no deaths were reported.
A case-control study suggested that four dry pet food brands were associated with Salmonella illnesses, and all were produced at the same plant. A Sep 4, 2007, CDC update on the outbreak said the contaminated dry dog food brands were produced by Mars Petcare, headquartered in Nashville.
On Aug 21, the company voluntarily recalled two of its products that in an environmental investigation yielded the outbreak strain. One was 5-lb bags of Krasdale Gravy dry dog food; the other was 50-lb bags of Red Flannel Large Breed Adult Formula dry dog food. However, MMWR reported that some of the brands that were linked to illnesses were not included in the recall.
"Because dry pet food has a 1-year shelf life and all contaminated products were not recalled, contaminated dry pet food might still be found in homes and could provide the potential for causing illness," the CDC reported.
The CDC said that, although an S Schwarzengrund source was never identified at the pet food plant, equipment may have been contaminated, or tainted ingredients may have entered the plant. Though the production of dry pet food usually involves heat treatment as the product is made, it is usually sprayed with a flavor enhancer such as an animal fat.
A spate of Salmonella outbreaks in humans has been connected to handling pet treats such as pig ears or food snacks, pet vitamins, and raw-food diets. However, the CDC said the S Schwarzengrund outbreak is the first to be associated with dry pet food.
The CDC advises people to wash their hands with warm soapy water for 20 seconds after handling dry pet food, treats, or supplements to avoid getting sick from contaminated pet food. It also advises keeping infants away from pet feeding areas and making sure young children don't touch or eat the items.
CDC. Multistate outbreak of human Salmonella infections caused by contaminated dry dog food—United States, 2006-2007. MMWR 2008;57(19):521-4 [Full text]
Sep 4, 2007, CDC update on Salmonella Schwarzengrund outbreak
Aug 28, 2007, CIDRAP news story "Outbreak strain of Salmonella found in dog food"