About Salmonella

Salmonella is one of the most common enteric (intestinal) infections in the U.S. In some states (e.g. Georgia, Maryland) it is the most common, and overall it is the second most common foodborne illness (usually slightly less frequent than a Campylobacter infection). The reported incidence of Salmonella illnesses are about 17 cases per each 100,000 persons.¹

Symptoms of Salmonella infection:

The acute symptoms of Salmonella gastroenteritis include the sudden onset of nausea, abdominal cramping, and bloody diarrhea with mucous. The onset of symptoms usually occurs within 6 to 72 hours after the ingestion of the bacteria.² The infectious dose is small, probably from 15 to 20 cells.

Salmonella infections usually resolve in five to seven days, and many times require no treatment, unless the patient becomes severely dehydrated or the infection spreads from the intestines. Persons with severe diarrhea may require rehydration, often with intravenous fluids. Treatment with antibiotics is not usually necessary, unless the infection spreads from the intestines, or otherwise persists, in which case the infection can be treated with ampicillin, gentamicin, trimethoprim/sulfamethoxazole, or ciprofloxacin. Some Salmonella bacteria have become resistant to antibiotics, however, and this has occurred possibly as a result of the use of antibiotics to promote the growth of feed animals.

What tests can be done to determine whether a person has Salmonellosis?

The diagnosis of salmonellosis is confirmed by cultures of stool or blood. Specimens of blood or feces are placed in nutrient broth or on agar and incubated for 2-3 days. After that time, a trained microbiologist can recognize Salmonella bacteria, if present, by its unique characteristics.

Blood cultures are often not performed and in most cases the blood stream is not infected. In the stool, the laboratory is challenged to pick out Salmonella from many other similar bacteria that are normally present. In addition, many persons submit cultures after they have started antibiotics, which may make it even more difficult for a microbiology lab to grow Salmonella. So, the diagnosis of salmonellosis may be problematic and many mild cases are culture negative.

CDC. Preliminary FoodNet Data on the Incidence of Foodborne Illnesses - Selected Sites, United States, 1999. MMWR, 2000; 49:210-205.
CDC. Guidelines for confirmation of foodborne-disease outbreaks. MMWR, 1996; 45: 59-66.