Shigella dysenteriae

Snapshot

• A 6-year-old girl is brought in to the emergency department for a 2-day history of fever and watery diarrhea.  This morning, the diarrhea contained some blood. She had just traveled to Bangladesh to visit relatives. According to her family, an uncle there recently had bloody diarrhea as well. On physical exam, she is febrile, has hyperactive bowel sounds, and abdominal tenderness to palpation. A stool culture and Gram stain reveals lactose-fermenting, gram – rods. She is admitted for immediate rehydration and treatment.

Introduction

• Classification 
  • Shigella spp.
    • a non-flagellated, non-lactose-fermenting gram – rod
    • oxidase – and does not produce H₂S
    • produces endotoxin and Shiga toxin
  • transmission
    • fecal-oral transmission
  • organisms
    • S. dysenteriae (produces the most toxin)
    • S. flexneri
    • S. boydii
    • S. sonnei (most common in the United States and least severe)
• Epidemiology
  • incidence
    • more common in developing countries
  • demographics
    • more common in children
  • risk factors
    • ingestion of contaminated or uncooked food/water
    • travel
    • poor hygiene
    • crowding
• Pathogenesis
  • infects gastrointestinal track through invasion of Peyer patch M cells 
    • resistant to gastric acid
  • does not spread hematogenously
  • Shiga toxin (enterotoxin)
    • “A” subunit inactivates 60S ribosome 
      • kills intestinal cells by inhibiting protein synthesis
    • neurotoxic, cytotoxic, and enterotoxic
    • produced by S. dysenteriae
• Associated conditions
  • shigellosis (bacillary dysentery)
  • reactive arthritis
• Prognosis
• symptoms occur a few days after exposure

Presentation

• Symptoms
  • fatigue
  • malaise
  • anorexia
  • tenesmus
  • watery diarrhea precedes bloody diarrhea 
    • bloody and mucoid stools 
  • abdominal pain or cramping
• Physical exam
  • fever
  • hyperactive bowel sounds
  • abdominal tenderness
• signs of dehydration

Studies

• Labs 
  • stool culture
• Making the diagnosis
• based on clinical presentation and laboratory studies

Differential

• Enteroin­vasive Escherichia coli (EIEC)
  • distinguishing factor
    • clinically very similar to shigellosis but typically less contagious and less severe
• distinguish based on culture or polymerase chain reaction

Treatment

• Management approach
  • antibiotics will shorten duration of dysentery 
  • choice of antibiotics ultimately depends on regional resistance patterns
  • anti-motility drugs should be avoided, as they may worsen symptoms
• Conservative
  • rehydration
    • indication
      • all patients
    • modalities
      • oral
      • intravenous
• Medical
  • antibiotics
    • indication
      • severe cases
    • drugs
      • ciprofloxacin
      • ceftriaxone
      • trimethoprim-sulfamethoxazole (TMP-SMX)
  • zinc
    • indication
      • young children
    • outcomes
      • shortens duration of disease in children
• also improves weight gain

Complications

• Reactive arthritis (Reiter syndrome)
  • classic triad of conjunctivitis, urethritis, and arthritis
• Febrile seizures