• Epidemiology
  1. Most common cause of bloody Diarrhea in the United States (since 2010 when surpassed E. coli 0157:H7)
  • Pathophysiology
  1. Characteristics
    1. Facultative Anaerobic Gram Negative Rod in Enterobacteriaceae family
      1. Grouped with SS Gram Negative Bacteria (Salmonella, Shigella)
    2. Humans are the only hosts for Shigella
      1. Shigella is not a normal colonizer of the human intestinal tract (always pathogenic)
    3. Distinguished from other Enterobacteriaceae
      1. Non-motile as it has no flagella (unlike E. coli, Enterobacter, Serratia, Salmonella, Citrobacter and Proteus)
      2. Does not ferment lactose (unlike E. coli)
      3. Does not produce Hydrogen Sulfide or H2S (unlike Salmonella)
  2. Mechanism of Toxicity
    1. Only small inoculum required for infection
    2. Invades Small Bowel mucosa
    3. Produces Enterotoxin (Shiga Toxin) in colon
      1. Similar to the Enterotoxin in Enteroinvasive E. coli and Enterohemorrhagic E. coli
      2. Two different Enterotoxins have been identified (ShET-1, ShET-2)
      3. A Subunit (Active)
        1. Deactivates 60S ribosome (at 28S rRNA)
        2. Inhibits Protein synthesis, thereby killing intestinal epithelial cells
      4. B Subunit (Binding)
        1. Five B subunits are attached to each A subunit
        2. B Subunits bind colon's microvillus membrane (at Glycolipid Gb3 receptor)
    4. Toxin results in exaggerated inflammatory response, resulting in colitis and dysentary
      1. Epithelial cells are sloughed off, leaving shallow ulcerations
      2. Fluid losses are related to intestinal cell injury, unable to reabsorb fluid and Electrolytes
  3. Transmission
    1. Occurs via items contaminated with human feces (Hand contact, Fly infestation)
    2. Foodborne Sources (fecal-oral route)
      1. Contaminated drinking water
      2. Contaminated raw produce
      3. Foods contaminated by infected food handler
    3. Sexually Transmitted Infection (anal sex)
      1. More common among Men who have Sex with Men
  4. Four serotypes
    1. Shigella sonnei
      1. Most common Shigella species causing Infectious Diarrhea in industrialized countries
    2. Shigella flexneri
      1. Most common Shigella species causing Infectious Diarrhea in tropical and subtropical regions
      2. Growing Incidence as a Sexually Transmitted Infection in the United States
        1. Associated with anal sex and oro-anal sex, and presents with severe Diarrhea
        2. Multi-drug resistant and treatment requires susceptibility testing
        3. Associated with HIV Infection
    3. Shigella dysenteriae
      1. Less common outside of South Asia and Sub-Saharian Africa
    4. Shigella boydii
      1. Less common outside of South Asia and Sub-Saharian Africa
  • Risk Factors
  1. Foodborne Sources (fecal-oral route)
    1. Preschool children
    2. Nursing Home residents
  2. Sexually Transmitted Infection (anal sex)
    1. Men who have Sex with Men
  • Symptoms
  1. Onset: 4 to 7 days (as early as 1-3 days in some cases)
  2. Duration: 24 to 48 hours
  3. Diarrhea (often severe)
  4. Tenesmus
  5. Abdominal cramps
  6. Nausea and Vomiting
  7. Lassitude
  8. Bloody stool (51% of cases)
  9. Stool mucus may be seen
  • Signs
  1. Fever (58% of cases)
  2. Dehydration
  3. Lower abdominal tenderness
  1. Hyperemic bowel wall
  2. Mural edema
  3. Purulent exudate
  • Labs
  1. Stool microscopy
    1. Stool Mucus
    2. Fecal Leukocytes present
  2. Complete Blood Count
    1. Leukocytosis or Leukopenia
  3. Routine Stool Culture
    1. Negative only after 48 hours of Antibiotics
  • Management
  1. See Acute Diarrhea
  2. Treat Immunocompromised patients for 7-10 days
  3. Trimethoprim-Sulfamethoxazole (Bactrim) is no longer recommended due to Antibiotic Resistance
  4. Adults with Dysentery: first-line agents
    1. Ciprofloxacin 500 mg orally twice daily for 3 days or
    2. Levofloxacin 500-750 mg orally daily for 3 days
  5. Adults with Dysentery: alternative agents
    1. Azithromycin 500 mg daily for 3 days or
    2. Ceftriaxone 1-2 g IV daily for 3 days (in severe disease)
  6. Children with Dysentery: first-line agents
    1. Azithromycin 10 mg/kg/day daily for 3 days or
    2. Ceftriaxone 50-75 mg/kg/day for 2- 5 days (in severe disease)
  7. References
    1. (2015) Sanford Guide to Antimicrobial Therapy, IOS app accessed 5/8/2016
  • Resources