How long do salmonella infections can last?

Depends: If this is salmonella typhi, it may colonize the gall bladder and then persist in stools for a very lengthy time period. If this was simply salmonella spp. Gastroenteritis you should eliminate it fairly quickly.

Agree with Dr. Raff: Uncomplicated cases usually resolve in 4 to 7 days. However complications like endocarditis (infection involving heart), Osteomyelistis (bone infection) & infection of brain/ spinal cord (meningitis) can lead to lengthy periods of illness.