Strep Infection: Invasive Group A β-Hemolytic Streptococcus
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Infection associated with isolation of group A β-hemolytic streptococci (GABHS) from a normally sterile body site; includes 3 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
- Hepatic involvement
- Adult respiratory distress syndrome
- A generalized erythematous macular rash that may desquamate
- 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.
- Overall mortality rates for invasive GABHS infections are lower in children (5–15%) than in adults (30–80%).
- Most cases occur in winter and early spring.
- It is estimated that the annual incidence in the United States is 1.5–5.9 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 for invasive GABHS infections include injuries resulting in bruising or muscle strain, surgical procedures, and viral infections such as varicella.
- 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.
- 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.
- 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.
- There may be no identifiable focus of infection.
Streptococcus pyogenes is the only species of β-hemolytic streptococci to be associated with invasive infections.