We have a great post on the topic of Salmonella and backyard chickens on our blog. You can also watch this YouTube video to see additional tips and advice:
Nonetheless, every so often it will be in the news that some people have gotten ill with Salmonella from eating tomatoes or spinach, for example--usually cases in which the food was contaminated by rodents in a warehouse somewhere.
Periodically, you may hear about Salmonella outbreaks traced back to factory farms producing eggs for grocery stores across the country. It is important to know that eggs laid in factory farm conditions can be very dirty and germy, so undercooking them can cause serious illness.
Our hatcheries are NPIP-certified, with flocks closely monitored per state NPIP regulations. (Our hatcheries are also monitored for the H5/H7 strains of AI.) But when it comes to issues with Salmonella, contamination is FAR more of an issue with factory farmed birds that produce eggs for grocery stores, not with your backyard pets. This is because the conditions chickens are are kept in at factory farms are simply terrible. (You can Google information about this if you have a strong stomach, but to give you an idea, some of the conditions birds are forced to endure in factory farms include having to share cages or space with--and lay eggs on--other dead and rotting birds.) Since salmonellosis is food poisoning, it isn't an illness that passes from person to person or hen to hen like a cold. When chickens contract Salmonella, it is usually the result of hens eating rat droppings or worse in their tiny, dirty spaces at commercial egg farms. Yuck.
Presuming you don't keep your hens in the same inhumane circumstances they are kept in at factory farms---that is, presuming your coop is clean and roomy and you provide fresh food and water for them at all times---it is doubtful your home flock would contract Salmonella. Birds in factory farms have immune systems that are already stressed by the terrible conditions they experience every day. At home, Salmonella illness in your hens is easy to prevent: keep the coop clean and your hens happy. And most importantly, be alert to sign of illness so that if there is a problem, you can take care of it. But do be aware that your hens don't have to be sick with Salmonella to transmit it to you. Remember, Salmonella and other bacteria can be present in small quantities the feces of animals (including dogs and cats) whether they are sick or not. 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.
A hen actually sick from Salmonella will be immediately obvious: she will be weak, purple-combed, and have watery diarrhea as well as reduced egg production. In fact, it's hard to imagine that all those sick hens went unnoticed at those factory farms for so long. Even if workers could not manage to differentiate the symptoms of Salmonella from all the other symptoms of distress that factory farmed chickens have routinely, surely they would have noticed the big drop in production. After all, even if factory farms don't care about the welfare of their birds, they DO care about production--it's what compels them to keep the birds in such terrible, dirty, cramped conditions in the first place. It's just cheaper.
If you are worried that your flock has somehow contracted this illness anyway, you should have your flock examined by a vet or tested. But in most cases, the eggs from your own backyard flock are probably the safest eggs you can eat. When you keep your own birds, you can personally monitor their health, and you can control what feed they eat and the conditions they live in. You can see when they may need medical attention, and you can provide it. Salmonella outbreaks at factory farms are another reason to keep your own hens. When you know anything about factory farms, you realize that the surprising thing here is not that there is an occasional outbreak; the surprising thing is that there aren't many, many more.