Salmonella is one of the most common infections in the United States. It's caused by gram-negative bacilli of the genus Salmonella, a member of the Enterobacteriaceae family. It occurs as enterocolitis, bacteremia, localized infection, typhoid fever, or paratyphoid fever. Nontyphoidal forms of salmonella infection usually produce mild to moderate illness, with low mortality. Enterocolitis and bacteremia are especially common (and more virulent) among infants, elderly people, and people already weakened by other infections, especially human immunodeficiency virus infection. Paratyphoid fever is rare in the United States.
Typhoid fever, the most severe form of salmonella infection, usually lasts from 1 to 4 weeks. The incidence of typhoid fever in the United States is increasing as a result of travel to endemic areas, especially the borders of Mexico. An attack of typhoid fever confers lifelong immunity, although the patient may become a carrier.
Salmonella enterocolitis can range from mild to severe diarrheal illness. The infection is acquired through ingestion of contaminated food or water. Any food can become contaminated during preparation if conditions and equipment for food preparation are unsanitary.
The incubation period is 8 to 48 hours after exposure, and the acute illness lasts for 1 to 2 weeks. The bacteria is shed in the feces for months in some treated patients. A carrier state exists in some people who shed the bacteria for 1 year or more following the initial infection.
Symptoms and Signs
Symptoms include such as:
In most cases, diagnosis requires isolating the organism in a culture, particularly blood (in typhoid or paratyphoid fever and bacteremia) or stool (in typhoid or paratyphoid fever and enterocolitis). Other appropriate culture specimens include urine, bone marrow, pus, and vomitus. In endemic areas, clinical symptoms of enterocolitis allow a working diagnosis before the cultures are positive. The presence of S. typhi in stools 1 or more years after treatment indicates that the patient is a carrier (about 3% of patients) .
Widal's test, an agglutination reaction against somatic and flagellar antigens, may suggest typhoid fever with a fourfold increase in titer. Drug use or liver disease also can increase these titers and invalidate test results. Other supportive laboratory values may include transient leukocytosis during the first week of typhoidal salmonella infection, leukopenia during the third week, and leukocytosis in local infection.
The type of antimicrobial agent chosen to treat typhoid fever, paratyphoid fever, or bacteremia depends on organism sensitivity. Choices include ampicillin, amoxicillin, chloramphenicol, ciprofloxacin, ceftriaxone, cefotaxime and, for the severely toxemic patient, cotrimoxazole. Localized abscesses may require surgical drainage. Enterocolitis requires a short course of antibiotics only if it causes septicemia or prolonged fever.
Symptomatic treatment includes bed rest and fluid and electrolyte replacement. Camphorated opium tincture, kaolin and pectin mixtures, diphenoxylate, codeine, or small doses of morphine can relieve diarrhea and control cramps for patients who remain active.
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