Of an estimated 1,700 serotypes of Salmonella, serotypes typhimurium and enteritidis are the most common in the United States. Nontyphoidal salmonellosis generally follows the ingestion of contaminated or inadequately processed foods, especially eggs, chicken, turkey, and duck. Cooking foods to an appropriate temperature reduces the risk of contracting salmonellosis. Other causes include contact with infected people or animals or ingestion of contaminated dry milk or drugs of animal origin. Salmonellosis may occur in children younger than age 5 via the fecal-oral route. Enterocolitis and bacteremia are common (and more virulent) among infants, elderly persons, and people already weakened by other infections; paratyphoid fever is rare in the United States.

Typhoid fever usually results from drinking water contaminated by the excretions of a carrier or from ingesting contaminated shellfish. (Contamination of shellfish occurs by leakage of sewage from offshore disposal depots.) Most typhoid patients are younger than age 30; most carriers are women older than age 50. The incidence of typhoid fever in the United States is on the rise as a result of increased travel to endemic areas.

Salmonellosis may result in such complications as intestinal perforation or hemorrhage, cerebral thrombosis, pneumonia, endocarditis, myocarditis, meningitis, pyelonephritis, osteomyelitis, cholecystitis, hepatitis, septicemia, and acute circulatory failure.

Clinical manifestations of salmonellosis vary but usually include fever, abdominal pain, and severe diarrhea with enterocolitis. Headache, increasing fever, and constipation are more common in typhoidal infection.