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Group Character
- Gram positive cocci that grow in chains
- No catalase
- Blood agar
- Beta hemolysis - clear zones around colonies in blood agar; classified by carbohydrate Ag (lancefield groups)
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Structure
- Cell wall built upon peptidoglycan matrix
- M protein: fibrillar coiled-coil molecule like myosin; extremely diverse in distal ends, conserved in middle portions; Ag receptor, binds fibrinogen, factor H, and others, and provides scaffold for LTA in pathogenesis
- LTA: binds to cell receptors
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Exotoxins
- Streptolysin O: pore-forming, antigenic which is basis of ASO test
- SuperAg toxings: 10% of GAS produce these; similar to Staph SuperAg
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Epidemiology
- Phygnitis: Most common cause in school age kids; person to person transmission via coughing, sneezing, etc...; 1-4 week duration
- Impetigo: Minor skin truame with GAS colonization
- Wound infections: iatrogenic
- STTS: Severe soft tissue invasion; rapid progression to death
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Pathogenesis
- Nasopharynx invasion
- M protein provides scaffold for LTA to reach binding site (in skin, M binds directly)
- Protein F - adherence to langerhans cells
- M protein prevents phagocytosis via binding factor H
- STSS: massive cytokine release
- ARF: Type II hypersensitivity; Ab to M protein
- Acute glomerula nephritis: Type III hypersensitivity
- Type specific immunity; type specific IgG activate complement via classical pathway
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Clinical Manifestations: Acute infection
- Pharyngitis: between 5-15 yo; acute sore throat, malaise, fever, headache; tonsillar pillars, uvula, soft palate; erythema, pus; cervival adenopathy; Self-limiting; can spread to form abcesses
- Impetigo: small vesicle w/ erythema; enlarges, yellow crust; 2-5 yo kids
- Erysipelas: Spreading erythema w/edema and fever
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Clinical Manifestations: StrepSAgs
- Scarlet Fever: buccal mucosa, temples, cheeks are deep red with circumural rash; strawberry tongue; sandpaper rash on second day of illness
- STSS: Begin at any site of infection; vague myalgia, chills, severe pain at site of infection; necrotizing fasciitis and myonecrosis; Continues with nausea, vomiting, hypotension, shock and organ failure
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Post Strep Sequelae
- ARF: Fever, carditis, subcutaneous nodules, chorea, and polyarthritis; murmurs, enlargement; 3 weeks post strep pharyngitis; last 2 weeks to 3 months; repeat attacks cause progressive heart damage
- Acute GN: Disease of childhood; begings 1-4 weeks after pharyngitis and 3-6 weeks post skin infection
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Diagnosis
- Clinical
- Blood agar with Beta hemolysis
- Serologix groupig
- Rapid strep test: group A Ag on throat swab
- ASO titers in ARF
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Treatment
- Pencillin G
- Treat within 10 days to prevent ARF
- Prophylaxis for recurrent ARF during ages 5-15 and during certain procedures
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