infectious disease salmonellosis

Infectious Disease Salmonellosis

Salmonellosis, named after pathologist Daniel S. Salmon who first isolated the organism from porcine intestine, was first described in 1880 and cultured in 1884 (Salmonellosis1 pp). Salmonellae are motile, gram-negative, rod-shaped bacteria of the family Enterobacteriaceae, and are common in the gastrointestinal tracts of mammals, reptiles, birds, and insects (Salmonellosis1 pp).

Salmonellae are potential enteric pathogens and a leading cause of bacterial food-borne illness (Salmonellosis1 pp).

With a single overarching species (Salmonella

choleraesuis) and over 2000 serotypes, salmonellae have been implicated in a spectrum of diseases, including enteric or typhoid fever (primarily

Salmonella typhi and Salmonella paratyphi), bacteremia, focal infections, and enterocolitis (typically Salmonella

typhimurium, Salmonella enteritidis, and Salmonella

heidelberg) (Salmonellosis1 pp).

Salmonellae is usually transmitted by consumption of contaminated foods, particularly beef, poultry, and eggs, although improperly prepared fruits, vegetable, dairy products, and shellfish have also been implicated, as well as human-to-human and animal-to-human transmission (Salmonellosis1 pp). The infectious dose varies among strains, however, a large inoculum is believed to be necessary to overcome stomach acidity and to compete with normal intestinal flora (Salmonellosis1 pp). Yet, lower infectious doses may be adequate to cause infection if these organisms are do-ingested with foods that rapidly transit the stomach, such as cheese and milk, or if antacids are used concomitantly, or if ingested by persons with impaired immune systems (Salmonellosis1 pp).

After ingestion, infection with salmonellae is characterized by attachment of the bacteria by fimbriae or pili to cells lining the intestinal lumen, then the bacteria are internalized by receptor-mediated endocytosis and transported within phagosomes to the lamina propria where they are released (Salmonellosis1 pp). Once there, salmonellae induce an influx of macrophages, typhoidal strains, or meutrophils, nontyphoidal strains, and although nontyphoid salmonellae generally precipitate a localized response, S typhi and other especially virulent strains invade deeper tissue via lymphatics and capillaries and elicit a major immune response (Salmonellosis1 pp).

In 1997, the estimated annual incidence of salmonellosis in the United States was 13.8 cases per 100,000 people, and the incidence is greatest among children and individuals who are institutionalized and nursing home residents (Salmonellosis1 pp). Salmonellae typically produces a self-limiting gastroenteritis, and dehydrated patients occasionally require hospitalization, however, death rarely occurs (Salmonellosis1 pp). Although uncommon, increased mortality rates are associated with extraintestinal complication of salmonellosis caused by seeding of bacteria to other organs, and include complications such as "endocarditis and arterial infections, cholecystitis, hepatic and splenic abscesses, urinary tract infections, pneumonia or empyema, meningitis, septic arthritis, and osteomyelitis" (Salmonellosis1 pp).

Salmonella infections generally produces one of three distinct syndromes, gastroenteritis, typhoid fever, or focal disease (Salmonellosis1 pp). Nontyphoidal salmonellae usually causes enterocolitis similar to that caused by other bacterial enteric pathogens (Salmonellosis1 pp). Nausea, vomiting, and diarrhea occur within six to forty-eight hours after ingestion of contaminated food or drink, and in most cases, stools are loose and bloodless and resolve within three to seven days (Salmonellosis1 pp). Salmonellae may also cause large-volume choleralike diarrhea or may be associated with tenesmus (Salmonellosis1 pp). An initial transient diarrhea may occur, however, established infections with S. typhi or S. paratyphi are associated with abdominal pain and either constipation or recurrent diarrhea (Salmonellosis1 pp). Also common are fever, abdominal cramping, chills, headache, and myalgia, with the fever usually resolving within forty-eight hours (Salmonellosis1 pp).

Determining whether Salmonella is the cause of illness depends on laboratory tests that identify Salmonella in the stools of an infected person (Salmonellosis pp). However, these tests are usually not performed unless the laboratory is instructed to look specifically for the organism (Salmonellosis pp). Once identified, further testing can determine its specific type and which antibiotics can could be used to treat it (Salmonellosis pp).

Salmonella gastroenteritis is usually a self-limiting disease with direct therapy at fluid and electrolyte replacement (Salmonellosis1 pp). Since antibiotics do not appear to shorten the duration of symptoms and actually prolong the duration of convalescent carriage, they are not used routinely to treat uncomplicated Salmonella gastroenteritis (Salmonellosis1 pp). The use of antibiotics are usually reserved for those with severe disease or high risk patients (Salmonellosis1 pp). If an antibiotic is required, treatment with an "oral quinolone, trimethoprim-sulfamethoxazole, or amoxicillin for 48-72 hours or until defervescence is usually adequate" (Salmonellosis1 pp). Chloramphenicol has been the treatment of choice for typhoid fever for more than 50 years because it is both inexpensive and effective, yet as a consequence of emerging drug resistance and bone marrow toxicity, the oral form of this drug is no longer available in the United States (Salmonellosis1 pp). The recommended oral regimens for treating typhoid fever include "amoxicillin, trimethoprim-sulfamethoxazole, or a fluoroquinolone" (Salmonellosis1 pp).