FDA investigators in October started taking samples of dry pet food, pet treats and diet supplements from distributors, wholesalers and retailers such as PetSmart, PetCo, Walmart, Costco, Sam's Club and Target.
The FDA said in a memorandum released this week it is "particularly concerned about salmonella being transmitted to humans through pet foods, pet treats, and supplements for pets that are intended to be fed to animals in homes, where they are likely to be directly handled or ingested by humans."
The testing covers dog and cat food but also feed for rabbits, reptiles, birds, aquarium fish and rodents such as hamsters, mice and guinea pigs.
People usually get salmonella poisoning by eating contaminated food, according to the Centers for Disease Control and Prevention (CDC). But it is also possible to get sick just "by putting objects or fingers contaminated with these germs into the mouth." Salmonella also can sicken pets who eat contaminated food.
The CDC advised consumers to wash their hands after feeding pets and keep infants away from the dog's dish.
The FDA pointed to CDC data that show 70 people got sick from January 2006 through December 2007 in connection with salmonella-tainted dry dog food produced in Pennsylvania.
That outbreak included a strain of the bacteria known as Schwarzengrund, according to the CDC. The strain is considered resistant to some antibiotics used to treat the infection.