Q: How is Salmonella infection transmitted to chickens in the first place?
A: You probably don't have to worry about well cared for backyard hens catching salmonella if you provide a clean environment for them. Hens in factory farms usually get infected because they have eaten rat droppings from the conveyor belt that carries their feed.
Apart from rat and rodent droppings, chicks can hatch ill with salmonella, having had it passed to them by their mothers. Chickens that are purchased at auctions, shows or other places may pass an illness into your own flock. Always buy from NPIP sources who monitor their flocks' health carefully. Our flocks are NPIP certified and test Salmonella-pullorum-typhoid clean, as are the flocks of most major hatcheries. Chickens that are ill with Salmonella can also pass it to other flock members if their waterers or feed get soiled with droppings--or they may even pass it along through feather dander. Please read about how to recognize the symptoms of salmonellosis in the related questions below.
But always remember, too, that your hens don't have to be sick with salmonella to pass bacteria to you, so when you pick up your bird who has been walking in and pecking around poopy litter, just wash your hands... the same way you'd wash your hands if your dog--who has been nibbling on canine-enticing cat poop in the yard--licks your fingers with doggy love. Use common sense.