Strep Infection: Invasive Group A β-Hemolytic Streptococcus

Basics

Description

Infection associated with isolation of group A β-hemolytic streptococci (GABHS) from a normally sterile body site; includes three clinical syndromes:

  • GABHS toxic shock syndrome (STSS)
  • GABHS necrotizing fasciitis (NF)
    • Infection characterized by extensive local necrosis of skin and subcutaneous soft tissues
  • Isolation of GABHS from normally sterile sites in patients not meeting criteria for STSS or NF (e.g., meningitis, osteomyelitis, septic arthritis, myositis, surgical wound infections) with or without bacteremia
    • Diagnostic criteria for STSS:
      • (I) Isolation of GABHS
        • A: From a normally sterile site (e.g., blood, CSF, tissue, peritoneal fluid)
        • B: From a nonsterile site (e.g., throat, vagina, sputum, open surgical wound)
      • (II) Clinical signs of severity
        • A: Hypotension
        • B: Two or more of the following signs:
          • Renal impairment
          • Coagulopathy
          • Hepatic involvement
          • Acute respiratory distress syndrome
          • A generalized erythematous macular rash that may desquamate
        • C: Soft tissue necrosis, including NF or myositis, or gangrene
    • A definite case fulfills criteria IA and II (A and B). A probable case fulfills criteria IB and II (A and B) and no other identifiable cause.

Epidemiology

  • Overall mortality rates for invasive GABHS infections are lower in children (3.6–8.3%) than in adults (30–80%).
  • Most cases occur in winter and early spring.

Incidence

  • The average annual incidence in the United States is approximately 3.5 cases per 100,000 persons.
  • Incidence is highest in infants and the elderly.
  • 85% of cases are sporadic, 10% hospital-acquired, 4% in chronic care facilities, 1% in cases with a close index contact.

Risk Factors

  • Risk factors for invasive GABHS infections include injuries resulting in bruising or muscle strain, surgical procedures, viral infections such as varicella, and use of NSAIDS.
  • High-risk groups include patients with diabetes mellitus, chronic cardiac or pulmonary disease, HIV infection or AIDS, and those with a history of IV drug use.

General Prevention

  • Routine immunization against varicella
  • Isolation of hospitalized patients
    • In addition to standard precautions, droplet precautions for children with pneumonia
    • Contact precautions should be used for at least 24 hours after the start of antimicrobial therapy in children with extensive or draining cutaneous infections.
  • Several GABHS vaccine candidates are in varying stages of development. A 26-valent recombinant M protein vaccine is the only vaccine to have entered into clinical trials.

Pathophysiology

  • The pathogenic mechanism has not been fully defined; however, an association with streptococcal pyrogenic exotoxins (SPE) has been suggested.
  • SPE A, B, and C (responsible for rash of scarlet fever) along with streptococcal exotoxins, mitogen factor, and superantigen stimulate activation of T lymphocytes and macrophages to produce large quantities of cytokines resulting in shock and tissue damage.

Etiology

Streptococcus pyogenes is the only species of β-hemolytic streptococci to be associated with invasive infections.

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