Dry dog, cat food associated with Salmonella outbreak

**Behravesh CB. Pediatrics. 2010; 126:e1-e7.**

A recent outbreak of salmonella highlights the importance of proper handling and storage of pet foods in the home to prevent human illness, especially among young children, according to a published study.

Researchers from the Pennsylvania Department of Health, the Ohio Department of Health, the CDC and the FDA initiated two case control-studies after being alerted to a multistate outbreak of Salmonella Schwarzengrund during 2007. Questionnaires were used to collect information on people’s contact with animals; the brands of dry dog or cat food purchased; handling and storage of the food and pet-feeding practices.

The first study sought to compare household factors of case-patients with those of controls. Illness was confirmed through laboratory testing, and cases included people who experienced gastrointestinal illness onset between Jan. 1, 2006, and Aug. 30, 2007.

The second study involved only children aged 2 years and younger who had regular dog contact in either their own homes or at another location. All children included in the study resided in Pennsylvania and were born between Jul. 1, 2005, and Jul. 20, 2007.

CDC researchers noted that 79 people in 21 states were infected with the outbreak strain during the 3-year period, and 48% were aged 2 years or younger. Thirty-eight percent of dog fecal specimens and 9% of dry dog food specimens taken from nine case-households in Pennsylvania contained evidence of the outbreak strain.

Two brands, dubbed A and B, produced by one Pennsylvania manufacturing plant were associated with these cases. Similar results were discovered by researchers in Ohio, although information on where the food was manufactured was unavailable.

In August 2007, the FDA discovered the outbreak strain in two other brands produced at the Pennsylvania plant. Upon inspection, one of 144 swab samples demonstrated contamination with the outbreak strain. Researchers also found evidence of the outbreak strain in more brands manufactured at the same plant in 2008.

Study data indicated a significant link between contact with a dog and Salmonella infection, the researchers noted, and members of case-households were also more likely to have purchased dry dog food, cat food or both manufactured at that particular plant.

The researchers’ findings led to two voluntary recalls of dry dog food, but additional outbreak-related illnesses eventually caused permanent closure of the plant.

“This investigation demonstrated that dry pet food may be contaminated with Salmonella and raises concerns that such contamination could be an underrecognized source of human infections, especially in young children,” wrote the researchers.

PERSPECTIVE

Salmonella ordinarily is a moderate dose enteric pathogen in which 1,000 to 100,000 viable cells must be ingested to produce disease. Secondary spread between people rarely occurs with strains of Salmonella because of the dose requirement. Most causes of intestinal salmonellosis involving older children and adults occur secondary to ingestion of contaminated foods where these inoculum sizes can be reached. For infants and young children, Salmonella infection can be acquired through ingestion of low organism doses (<1,000 cells). In the United States, the age group with the highest rate of salmonellosis are the infants < 12 months that result from household cross contamination. The study by Behravesh et al linking human Salmonella infections to contaminated dry dog and cat food show the infectivity of non-typhoid salmonellosis for young children in the household and underscore the potential for household spread of this important pathogen

– Herbert L. DuPont, MD

St. Luke's Hospital, Houston