Did you know? Salmonella was named after an American scientist named Daniel Elmer Salmon, who in 1885 first discovered a strain of the bacteria in pigs.
Species Name: Salmonella enteritidis and Salmonella typhimurium (which is actually a subgroup of S. enteritidis) are the most common species that cause gastroenteritis (diarrhea) in humans, but other disease-causing species exist, including Salmonella typhi, the cause of typhoid fever.
Type of Microbe: Gram-negative bacteria
How it spreads: Food-borne disease, spread by ingestion of foods contaminated with animal feces. Contaminated foods include beef, poultry, milk and eggs, but even vegetables and fruits are prone to contamination. Some household pets, including reptiles (turtles, lizards and snakes) and birds (especially baby chicks), may also carry Salmonella enteritidis.
Who’s at risk? All people, especially the very young and the elderly. The number of reported infections is highest in infants at 3 months of age. Infections are more common in the summer than winter.
Epidemiology: More than 40,000 cases are reported in the United States every year, but the actual number of cases, including milder or undiagnosed cases, is estimated at 2 to 4 million. Approximately 400 people die every year from the disease.
Symptoms: Within 8 to 72 hours of ingestion, symptoms of diarrhea (usually nonbloody), nausea, vomiting, abdominal pain and fever typically last 2 to 7 days.
Diagnosis: Gram-stain and culture of stool
Prognosis: Most infections are self-limited and resolve within 5 to 7 days. If the infection spreads to the blood stream and other organs, though, it may become fatal without antibiotic treatment.
Treatment: Oral rehydration is usually the only treatment necessary, although more severe cases may be treated with antibiotics.
Prevention: Avoid raw or undercooked eggs, poultry or meat. Drink only pasteurized milk and dairy products. Thoroughly wash all fruits and vegetables, including those with inedible rinds or skins. Practice good food preparation and dining habits. Wash hands after handling animals and their feces. Monitor young children around pets, and make sure the hands are cleaned also.
How it causes disease: After Salmonella enteritidis is ingested with contaminated food, it penetrates cells in the small intestine, causing the immune system to activate an inflammatory response. It is unclear exactly how Salmonella enteritidis causes diarrhea, but it is likely a combination of the invasion of the intestinal tissue and subsequent inflammation.
Immune response: Inflammation in the intestines
Complications: A small percentage of afflicted individuals develop Reiter’s syndrome, characterized by joint pain, eye irritation and painful urination that can last for months to years and develop into a chronic arthritis.
Sources:
Salmonella spp. USFDA Bad Bug Book. Center for Food Safety and Nutrition.
Salmonella. Centers for Disease Control and Prevention
