What is Salmonella? Salmonella is a bacteria that makes people sick. It was discovered by an American scientist named Dr. Salmon, and has been known to cause illness for over 125 years. The illness people get from a Salmonella infection is called salmonellosis. Most people infected with Salmonella develop diarrhea, fever, and abdominal cramps between 12 and 72 hours after infection. The illness usually lasts 4 to 7 days, and most individuals recover without treatment.