## Microbiology of Peritonsillar Abscess **Key Point:** Group A Streptococcus (GAS) is the most common causative organism in peritonsillar abscess, accounting for approximately 40–50% of cases. ### Frequency of Causative Organisms | Organism | Frequency | Clinical Notes | |----------|-----------|----------------| | Group A Streptococcus | 40–50% | Most common; β-hemolytic | | Staphylococcus aureus | 15–20% | Rising incidence, especially MRSA | | Anaerobes (mixed flora) | 20–30% | Peptostreptococcus, Prevotella | | Haemophilus influenzae | 5–10% | Less common in post-vaccination era | | Candida albicans | Rare | Only in immunocompromised patients | **High-Yield:** The majority of peritonsillar abscesses are polymicrobial, but GAS remains the single most frequently isolated aerobic pathogen. ### Pathogenesis 1. Acute bacterial pharyngitis (usually GAS-induced) 2. Infection spreads to tonsillar crypts and surrounding tissue 3. Localized suppuration and abscess formation 4. Unilateral presentation with trismus, dysphagia, and "hot potato" voice **Clinical Pearl:** The classic triad of peritonsillar abscess is unilateral swelling, soft palate deviation (away from abscess), and uvular deviation (toward abscess). This distinguishes it from simple acute tonsillitis. **Mnemonic:** **GASEOUS** — Group A Streptococcus is the most common Aerobic organism causing peritonsillar abscess, though Staphylococcus and anaerobes are also significant. ### Treatment Implications **Key Point:** Initial empiric antibiotic therapy should cover GAS and Staph aureus: - **First-line:** Amoxicillin-clavulanate or Cephalosporin (3rd generation) - **Penicillin-allergic:** Clindamycin (covers anaerobes too) - **MRSA risk:** Add vancomycin or linezolid Drainage (needle aspiration or incision and drainage) is indicated when fluctuance is present, as in this case.
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