Description

• Disease caused by any serotype of the bacterial genus Salmonella, a gram-negative bacilli
• Salmonellla enterica:
  • 2,500 different serotypes
  • Most pathogenic species in humans
• Nontyphoidal Salmonella has a number of agricultural animal hosts and is an important cause of foodborne infection.
• Clinical syndromes:
  • Gastroenteritis (75%)
  • Bacteremia (10%)
  • Enteric fever (10%) (see “Typhoid Fever”)
  • Localized infection outside GI tract (5%)
  • Chronic carrier state (<1%)
• Pathogenesis: Organisms are ingested, invade the gut mucosa, and produce inflammatory and cytotoxic response. They can then disseminate into systemic circulation via the lymphatic system.
• Chronic carrier state is defined as a positive stool culture >1 year.

Geriatric Considerations
Patients >65 have increased risk of developing invasive disease (1). This population often has comorbidities (atherosclerotic endovascular lesions, prostheses, etc.) that increase risk of seeding and bacteremia.

Pediatric Considerations
Neonates (<3 months) are more susceptible to invasive disease and subsequent complications, including CNS infection.

Pregnancy Considerations
Pregnancy has not been demonstrated to increase the risk or severity of infection.

Epidemiology

• Incidence of laboratory-confirmed Salmonella infection in 2009 in the US (2):
  • 16.47 cases per 100,000 in 2011 according to the CDC
  • Highest incidence in children <4 years
  • Hospitalization rates for infection are higher in patients ≥50
• Peak frequency: July–November
• Salmonella is second to Campylobacter as the major cause of bacterial diarrheal illness in the US
• Salmonella is also a common cause of traveler’s diarrhea.

Risk Factors

• Recent travel outside the US
• Chicken and egg consumption
• Contact with reptiles or live poultry:
  • In 2012, 6 multistate outbreaks were related to small turtles ( http://www.cdc.gov/salmonella/small-turtles-03-12/).
• Alteration of endogenous bowel flora (e.g., after antimicrobial therapy or surgery)
• Impaired gastric acidity: H₂ receptor blockers, antacids, PPIs, gastrectomy, achlorhydria
• Reticuloendothelial blockade: Sickle cell, malaria, bartonellosis
• Immunosuppression: AIDS, diabetes, corticosteroid use, immunosuppressant use, chemotherapy

General Prevention

• Proper hygiene in production, transport, and storage of food (e.g., refrigerating eggs to minimize multiplication of the bacteria if present, thoroughly cooking eggs prior to consumption)
• Control of animal reservoir, especially by avoiding contact with animal feces and polluted waters
• Hand hygiene
• Outbreak information available on CDC web site

Etiology

• Ingestion of contaminated food (e.g., poultry, beef, eggs, tomatoes, dairy products, commercially prepared nuts and nut products) or water accounts for 95% of cases (3).
• Person-to-person and/or fecal–oral spread
• Contact with chronic carrier (daycare center)
• Contact with exotic pets with high fecal carriage rates for Salmonella, especially reptiles
• Iatrogenic contamination (e.g., blood transfusion, endoscopy)

Commonly Associated Conditions

• Gastroenteritis: Typically associated with normal immune function
• Bacteremia: More often seen in immunocompromised patients or those with anatomic disruptions (e.g., cholelithiasis, prostheses)