Description

• Infection caused by any serotype of the bacterial genus Salmonella, a gram-negative facultatively 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 (i.e., osteomyelitis, abscess)

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 (mostly foodborne)
  • Wide variation by region from 40 to 3,980 estimated cases per 100,000
• Global incidence of invasive nontyphoidal Salmonella infection estimated to be 535,000 cases in 2017
• Most commonly identified foodborne bacterial illness in the United States and a common cause of traveler’s diarrhea.
  • Estimated 1.4 million cases per year in the United States, with annual incidence of 15 illnesses per 100,000
• Second most common bacteria isolated from stool cultures in diarrheal illness (following Campylobacter) in the United States
• Highest incidence of bacteremia 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 but can be lower in patients taking antibiotics or in the setting of gastric acid reduction.
  • 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
• Impaired phagocytic function: chronic granulomatous disease, hemoglobinopathies, malaria
• 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