A 28-year-old woman from Delhi presents to the emergency department with a 2-day history of severe pharyngitis, fever (39.5°C), and difficulty swallowing. On examination, she has exudative pharyngitis, enlarged tonsils with purulent exudate, and tender anterior cervical lymphadenopathy. A rapid antigen detection test (RADT) for Streptococcus pyogenes is positive. She has no history of penicillin allergy. What is the most appropriate immediate next step in management?

Explanation

## Management of Acute Streptococcus pyogenes Pharyngitis ### Clinical Context This patient presents with classic acute streptococcal pharyngitis (exudative pharyngitis, fever, cervical lymphadenopathy) and has a positive RADT, which is highly specific (>95%) for Group A Streptococcus (GAS). ### Why Immediate Antibiotic Therapy? **Key Point:** A positive RADT in a symptomatic patient is sufficient to initiate treatment immediately — throat culture confirmation is not required before starting antibiotics. **High-Yield:** RADT has: - Sensitivity: 85–90% - Specificity: >95% - Negative predictive value: ~99% when clinical suspicion is low Waiting for culture results (which take 24–48 hours) delays treatment and increases risk of: - Acute rheumatic fever (ARF) — prevented by antibiotics started within 9 days of symptom onset - Post-streptococcal glomerulonephritis (PSGN) — cannot be prevented by antibiotics - Suppurative complications (abscess, mastoiditis) ### First-Line Antibiotic Choice **Key Point:** Penicillin V (oral) or Penicillin G (intramuscular) is the gold standard for GAS pharyngitis. | Parameter | Penicillin V (Oral) | Amoxicillin (Oral) | Cephalexin (Oral) | |-----------|-------------------|-------------------|-------------------| | **Dose** | 500 mg QID × 10 days | 500 mg BID × 10 days | 500 mg QID × 10 days | | **First-line?** | Yes | Yes (equivalent) | If β-lactam allergy (non-IgE mediated) | | **Compliance** | Lower (QID dosing) | Better (BID dosing) | Good | **Clinical Pearl:** Amoxicillin is increasingly preferred in clinical practice due to better palatability and twice-daily dosing, though penicillin V remains the textbook standard. ### Why Not the Other Options? **Throat culture:** Not needed when RADT is positive and patient is symptomatic. Culture is reserved for: - Negative RADT with high clinical suspicion - Epidemiological surveillance - Recurrent infections **Abdominal ultrasound:** Splenic rupture is a rare complication of infectious mononucleosis (EBV), not GAS pharyngitis. This patient has no splenomegaly mentioned. **IVIG:** Prophylaxis for post-streptococcal sequelae is not indicated at acute presentation. Secondary prophylaxis (long-term penicillin) is given AFTER ARF has been diagnosed, not to prevent it in acute pharyngitis. ### Duration and Follow-up **Key Point:** Full 10-day course is mandatory to eradicate GAS and prevent ARF, even if symptoms resolve earlier. **Mnemonic: RADT-Positive = Treat Immediately** — Rapid Antigen Detection Test positive = Do not delay for culture = Treat immediately with penicillin.