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 was 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 was 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
  • Estimated 25,000 hospitalizations and 420 deaths per year (1)[A]
• 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.
• 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

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 (https://www.cdc.gov/salmonella/index.html)

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