Salmonella exists in the environment. Sorry but that is the way it is. There are a lot of different varieties of salmonella and a lot of them can make you sick. Freezing does not kill them. Heating above a certain temperature for a certain length of time will, length of time depends on how hot. They do need a digestive tract to reproduce but some can last a long time, even if totally dried out. Healthy human adults would need to ingest a relatively large quantity of salmonella to have a dangerous reaction but small children, the elderly, or weakened adults are at more risk.
If your chickens or other warm blooded animals are not infected with a dangerous variety of salmonella they are not a salmonella risk. If they are infected salmonella will be in their poop. Chickens walk in poop, they squat or lay down in poopy bedding or soil, they dust bathe in soil that has poop in it. If you touch a chicken with salmonella you can become infected. The same thing is true of your pet dog if you let it roll outside where a warm-blooded animal may have pooped. That's why the CDC recommends you wash your hands after handling any animal before you put the hands in your mouth. If your chickens are infected with a dangerous variety of salmonella you are probably in more danger from handling your chickens or their eggs that have touched their feathers than you are from putting chicken manure compost on your garden.
But lets get realistic. There are different levels of risk. A piece of space junk could fall out of the sky and hit your house. It happened in Australia a few years back (no one was hurt) so it could happen. You might have a fender bender the next time you go to the grocery. It might rain where you are today.
How many people do you read about on here that handle their chickens, snuggle with them, or even kiss them and then come down with salmonella? Basically none. I'd put the chances of you coming down with salmonella from handling your chickens above space junk but well below fender fender status, the more you wash your hands the better your odds. I'd put the odds of getting salmonella from putting chicken manure compost on your vegetable garden way below that, practically non-existent but possible. If a songbird splats your lettuce and you don't wash it really well you could get it from that.
I recognize that salmonella is in the environment but I don't live my life in fear because of that risk any more than I worry about space junk falling out of the sky and hitting me. I don't even look up to see if any space junk is on the way but I do regularly wash my hands. The benefits of that compost far outweigh the risks.