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Nontyphoidal Salmonellosis

Definition

  • An infection caused by ingestion of nontyphoidal salmonellae
  • Causes gastroenteritis, which may be complicated by bacteremia and or localized infection
  • Nontyphoidal salmonellosis is acquired from multiple animal reservoirs.

Epidemiology

  • Incidence
    • Has doubled over the past 2 decades (in U.S.)
    • U.S. Centers for Disease Control and Prevention (CDC) estimates 2 million cases annually, with 500 to 2000 deaths.
    • Seasonal association, with peak in food-borne outbreaks
      • Tropical climates: highest during rainy season
      • Temperate climates: highest during warmer months
  • The main mode of transmission is from food products contaminated with animal products or waste.
    • Most commonly transmitted through eggs and poultry
    • Also transmitted through undercooked meat, unpasteurized dairy products, seafood, and fresh produce
  • The majority of the reported cases in the U.S. are caused by Salmonella typhimurium or S. enteritidis.
    • S. enteritidis is associated with chicken eggs, whose contents are contaminated before shell deposition.
      • ~1 in 20,000 eggs is thought to be infected.
      • Between 1974 and 1994, the isolation of S. enteritidis from eggs in the U.S. increased 5-fold (from 5%–25%).
      • In 1998, the U.S. Department of Agriculture estimated that 80% of all salmonellosis cases were caused by infected eggs.
  • Centralization of food processing and widespread distribution of contaminated foods contribute to the increased incidence of nontyphoidal salmonellosis in developed countries.
  • Exposure to pets, especially reptiles, is a less common source of infection.
    • Fecal carriage rates in reptiles can be >90%.
    • Since 1986, an increase in popularity of unbanned reptiles, including iguanas, has been followed by increases in Salmonella infection rates.
    • Other pets, including African hedgehogs, snakes, birds, rodents, baby chicks, ducklings, dogs, and cats, can also serve as potential vectors.
  • Antibiotic resistance is increasing.
    • S. typhimurium of definitive phage type 104 (DT104)—a serotype resistant to ampicillin, chloramphenicol, streptomycin, sulfonamides, and tetracyclines—is prominent in the United Kingdom.
      • The prevalence of S. typhimurium DT104 in the U.S. increased from 0.6% in 1979–1980 to 34% in 1996.
      • In 1997, S. typhimurium DT104 strains resistant to ciprofloxacin (14%) or trimethoprim (24%) were isolated in the United Kingdom.
    • Ceftriaxone- and fluoroquinolone-resistant nontyphoidal Salmonella strains have increased in the U.S.
      • The CDC reported that the prevalence of ceftriaxone-resistant strains increased from 0 to 0.5% from 1995–1998.
    • The source of these resistant strains appears to be livestock treated with antibiotics.

Risk Factors

  • Risk factors for gastroenteritis
    • Conditions that decrease stomach acidity
      • Age of < 1 year
      • Antacid ingestion
      • Achlorhydric disease
    • Conditions that decrease intestinal integrity
      • Inflammatory bowel disease
      • History of GI surgery
      • Alteration of intestinal flora by antibiotic administration
  • Risk factors for bacteremia
    • Infancy
    • Advanced age
    • Severe underlying infection
    • Immunosuppression
  • Risk factors for complications with localized infection
    • Intraabdominal infections
      • Anatomical abnormalities of the hepatobiliary tree, including gallstones
      • Abdominal malignancy
      • Sickle cell disease
    • Central nervous system infections
      • Meningitis usually seen in neonates (< 4 months old)
    • Pulmonary infections
      • Preexisting abnormality of lung or pleura, including malignancy
      • Sickle cell disease
      • Glucocorticoid use
    • Urinary tract infections
      • Malignancy
      • Urolithiasis
      • Structural abnormalities
      • Immunosuppression
    • Bone and joint infections
      • Sickle cell disease
      • Hemoglobinopathies
      • Preexisting bone disease (fractures)
    • Reactive arthritis
      • In persons with HLA-B27 histocompatibility antigen
    • Soft tissue infections
      • Immunosuppression, localized trauma
  • Highest morbidity and mortality risks among:
    • Elderly
    • Infants
    • Immunocompromised patients
      • HIV infection
      • Blockade of reticuloendothelial system
        • Bartonellosis
        • Malaria
        • Schistosomiasis
        • Histoplasmosis

Etiology

  • More than 200 serovars of Salmonella are human pathogens.
  • Most infections in the U.S. are due to S. typhimurium or S. enteritidis.
  • Infection is acquired from multiple animal reservoirs via ingestion of contaminated food/water.
    • Infectious dose of Salmonella: 103–106 colony-forming units
    • Once organisms reach the small intestine, they penetrate the small-intestinal mucosa and traverse the intestinal layer through cells within Peyer’s patches.
    • Nontyphoidal Salmonella gastroenteritis is characterized by massive polymorphonuclear leukocyte infiltration into both the large- and the small-bowel mucosa.
    • The degranulation and release of toxic substances by neutrophils may result in damage to the intestinal mucosa, causing the inflammatory diarrhea observed with nontyphoidal gastroenteritis.

Associated Conditions

  • See Risk Factors.

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Last updated: March 13, 2008
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