According to the World Health Organization, salmonella poisoning is one of the most common food-borne illnesses around the world. Approximately 40,000 cases are reported to the Centers for Disease Control each year. More than 2,500 types, or "serovars," of salmonella have been identified to date; of these, approximately 2,000 are categorized as Salmonella enterica (SE). SE species live in the gastrointestinal tract of humans and animals. Characteristics of the most common disease-causing SE serovars in humans are discussed below.
Salmonella Enteridis
Salmonella enteridis (SEd) and Salmonella typhimurium (ST) are the two most common causes of salmonellosis in humans. Classic salmonellosis is a mild, self-limited gastroenteritis. Symptoms including fever, stomach cramps, nausea, vomiting and diarrhea typically appear within 12 to 72 hours of ingestion and resolve within four to seven days. Young children, the elderly and people with medical problems may require hospitalization for dehydration. Antibiotics are required in 2 percent of cases.
Rarely, SEd or ST escapes the intestine and enters the bloodstream. Bloodstream infection may be fatal and can produce long-term complications when bacteria leave the bloodstream to infect other areas of the body. Long-term complications of SE infections include infection of the heart valves and lining of the heart (endocarditis), brain abcess, infection of the bone (osteomyelitis) and Reiter's Syndrome, an autoimmune disease that produces chronic joint pain, eye irritation and problems with urination. These complications rarely occur in healthy adults. Almost all cases occur in immunocompromised people (AIDS, cancer and sickle cell anemia) or people with multiple medical problems.
SEd appears to colonize the gastrointestinal and reproductive tracts of poultry. The infection is passed to humans through food, while the animals remain asymptomatic. In fact, SEd infection actually appears to increase egg production. Approximately 80 percent of cases are traced to undercooked eggs.
Salmonella Typhimurium
The symptoms, course and complications of ST are indistinguishable from SEd. ST may be distinguished from SEd by laboratory tests and, often, patient history. Compared to SEd, ST is widely distributed among animal species. Infection has been reported from eating contaminated meat, game, poultry and unpasteurized dairy products. In 2008 and 2009, a multi-state outbreak of ST occurred when contaminated peanut butter was distributed to schools, nursing homes and snack-food manufacturers. In addition to food sources, ST infection can be transmitted through exposure to the feces of household pets including cats, dogs, amphibians such as frogs and reptiles such as turtles. The CDC recommends that people living with children under 5, the elderly or people with certain kinds of medical problems should not keep amphibians and reptiles as pets.
Salmonella Typhi
Salmonella typhi is the causative agent of typhoid fever, which may be transmitted through contamination of drinking water by urine or feces from infected animals and humans. Unlike other Salmonella enterica serovars, human-to-human transmission is common. Typhoid fever, also called "enteric fever," usually develops one to three weeks after exposure and varies in severity. Symptoms include high fever, weakness, lethargy, muscle pain, headache, loss of appetite and diarrhea or constipation. Pink spots appear on the chest; examination will usually reveal enlargement of the liver and spleen. In severe cases, symptoms of altered mental status and meningitis (fever, stiff neck, seizures) have been reported. Mortality approaches 10 percent without treatment and may be reduced to less than 1 percent with appropriate antibiotics.
