Streptococcal Disease (Invasive)

Basics

Description

  • Streptococcus pyogenes or group A Streptococcus (GAS) is a gram-positive coccus
  • It is responsible for noninvasive (pharyngitis, scarlet fever, impetigo) and invasive disease
  • Invasive disease occurs when GAS is isolated from a normally sterile site (cellulitis, necrotizing fasciitis (NF), pneumonia, streptococcal toxic shock syndrome (STSS), osteomyelitis, meningitis, bacteremia, arthritis, myositis, and endocarditis)
  • Most common portal of entry is the skin (50%) or respiratory system. Bacteremia without a source occurs in 15% of cases
  • Predisposing factors include viral illnesses (influenza, varicella), skin injury from trauma, immunodeficiency, malignancy, and extremes of age
  • May affect otherwise healthy patients who do not have underlying predisposing diseases
  • Rapid progression of shock and multiorgan dysfunction, with death occurring within 1–2 d
  • Incidence is 6/100,000 in industrialized countries
  • Rate of invasive GAS disease is 6 times the annual incidence of meningococcal disease
  • STSS, is a potentially fatal toxin-mediated condition triggered by GAS superantigens that activate the immune system
  • In STSS, portal of entry is unknown in 50% of cases

Stss Case Definition

  • Isolation of GAS from sterile or nonsterile body site
  • Hypotension
  • 2 or more of the following:
    • Fever (>38.5 °C)
    • Rash (diffuse macular erythema with subsequent desquamation)
    • Renal impairment
    • Coagulopathy (platelets <100 or DIC)
    • Liver abnormalities
    • Acute respiratory distress
    • Extensive tissue necrosis (NF)

Etiology

  • Occurs when susceptible host is infected with a virulent strain
  • GAS is causative in 10% of cases of NF. Blunt trauma is risk factor
  • Occurs sporadically with occasional outbreaks in long-term care facilities and hospitals
  • M protein within the bacterial cell wall is crucial for virulence, capable of binding host epithelial cells (allowing colonization) and providing protection from immune responses such as phagocytosis
  • Pyrogenic exotoxins that act as superantigens and produce fever and shock via activation of tumor necrosis factor and interleukins (similar to Staphylococcus aureus). The intense inflammatory cascade is responsible for the clinical features of STSS

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