Salmonella Infection

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Basics

Description

  • Infection caused by any serotype of the bacterial genus Salmonella, a gram-negative anaerobic bacillus
  • Nontyphoidal Salmonella typically causes gastroenteritis via foodborne infection and sporadic outbreaks; less commonly causes infection outside the gastrointestinal (GI) tract
  • Clinical syndromes
    • Enteric fever (see “Typhoid Fever”)
    • Nontyphoidal gastroenteritis
      • Chronic carrier state (>1 year)
    • Nontyphoidal invasive disease
      • Bacteremia
        • Endovascular complications
        • Localized infection outside GI tract

Geriatric Considerations
Patients >65 years old have increased risk of invasive disease with bacteremia and endovascular complications due to comorbidities (atherosclerotic endovascular lesions, prostheses, etc.) that increase risk of bacterial seeding.

Pediatric Considerations
Neonates (<3 months) are more susceptible to invasive disease and complications.

Epidemiology

Incidence
  • Global incidence of nontyphoidal Salmonella enteritidis estimated to be ~94 million per year
    • Wide variation by region from 40 to 3,980 estimated cases per 100,000
  • Global incidence of invasive nontyphoidal Salmonella infection estimated to be 2 to 6.5 million in 2010
    • Wide variation by region from 0.8 to 227 estimated cases per 100,000
  • Most commonly identified foodborne illness in the United States and a common cause of traveler’s diarrhea. Annual incidence in the United States is 15 illnesses per 100,000.
  • Second most common bacteria isolated from stool cultures in diarrheal illness (following Campylobacter) in the United States
  • Highest incidence in children <5 years old
  • Hospitalization rates higher in patients >50 years old
  • Peak frequency: July to November

Etiology and Pathophysiology

  • Salmonella enterica
    • Most pathogenic species in humans
    • 2,500 different serotypes
  • Etiology
    • ~95% of cases are foodborne.
    • Other cases (5%) are due to direct or indirect fecal–oral contact with animals or human carriers.
    • Iatrogenic contamination (e.g., blood transfusion, endoscopy) is rare.
  • Pathophysiology
    • Typical infectious dose in immunocompetent patients is ingestion of 1 million bacteria.
    • Bacteria ingested invade the distal ileal and proximal colonic mucosa to produce an inflammatory and cytotoxic response.
    • Bacteria can enter the mesenteric lymphatic system and then the systemic circulation to cause disseminated/invasive disease.

Risk Factors

  • Recent travel to underdeveloped nations
  • Consumption of undercooked meat, egg, or unpasteurized dairy products. Nonanimal products have also been implicated in outbreaks.
  • Contact with live reptiles or poultry
  • Contact with human carrier (Salmonella fecal shedding)
  • Impaired gastric acidity: H2 receptor blockers, antacids, proton pump inhibitors (PPIs), gastrectomy, achlorhydria, pernicious anemia, infants
  • Recent antibiotic use
  • Reticuloendothelial blockade: sickle cell disease, malaria, bartonellosis
  • Immunosuppression: HIV, diabetes, corticosteroid or other immunosuppressant use, chemotherapy
  • Iron overload, chronic granulomatous disease
  • Age <5 years or >50 years

General Prevention

  • Proper hygiene in production, transport, and storage of food (e.g., refrigeration during food storage and thoroughly cooking food prior to consumption)
  • Control of animal reservoirs: Avoid contact with high-risk animals, feces, and polluted waters.
  • Hand hygiene
  • CDC tracks outbreaks (http://www.cdc.gov/salmonella/).

Commonly Associated Conditions

  • Gastroenteritis
  • Bacteremia: immunocompromised or patients with underlying disease (e.g., cholelithiasis, prostheses)
  • Osteomyelitis: higher incidence in sickle cell disease
  • Abscesses: higher incidence with malignant tumors
  • Reactive arthritis

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