The symptoms generally appear 12 to 36 hours after exposure, but they can occur as quickly as six hours or as. long as 72 hours after exposure. In some instances, incubation periods of up to 16 days are possible. How is Salmonella spread? Salmonella live in the intestinal tracts of humans and other animals, including birds. People can become infected by ingesting food or water contaminated with Salmonella or after contact with infected animals.