## Microbiology of Acute Bacterial Tonsillitis **Key Point:** Group A beta-hemolytic streptococcus (GABHS / Streptococcus pyogenes) is the most common bacterial cause of acute tonsillitis in children and young adults. ### Common Causative Organisms | Organism | Frequency | Age Group | Clinical Notes | |----------|-----------|-----------|----------------| | Group A Streptococcus | 30–50% | Children, adolescents | Most common; risk of sequelae (rheumatic fever, PSGN) | | Streptococcus pneumoniae | 10–15% | All ages | Less common; vaccine coverage improving | | Haemophilus influenzae | 5–10% | Children < 5 years | Declining with Hib vaccination | | Staphylococcus aureus | < 5% | Post-intubation, immunocompromised | Rare in community-acquired tonsillitis | | Viral (EBV, RSV, rhinovirus) | 50–80% | All ages | Most common overall; self-limited | **High-Yield:** GABHS is the ONLY bacterial pathogen associated with non-suppurative sequelae — acute rheumatic fever (ARF) and post-streptococcal glomerulonephritis (PSGN). This is why rapid diagnosis and penicillin therapy are critical. **Clinical Pearl:** Throat culture remains the gold standard for diagnosis, though rapid antigen detection tests (RADTs) are widely used for point-of-care screening in clinical practice. **Mnemonic:** **GAP** = Group A (Streptococcus) is Primary cause of bacterial tonsillitis. 
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