Group A Streptococcal Pharyngitis
GAS bacterial pharyngitis — diagnose with RADT/culture and treat with penicillin to prevent rheumatic fever.
Also known as: GAS pharyngitis, strep throat, group A strep, streptococcal pharyngitis
Overview
Acute pharyngitis caused by Streptococcus pyogenes (group A beta-hemolytic Streptococcus, GAS). Distinguished from far more common viral pharyngitis by clinical features supported by rapid antigen detection test (RADT) and/or throat culture.
Epidemiology
GAS causes 15-30% of pharyngitis in children and 5-15% in adults. Most common in children 5-15 years. Peak in late winter/early spring. Spread by respiratory droplets; incubation 2-5 days. Asymptomatic carriage 5-20% in school-age children.
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Risk factors
- School-age children (5-15 years)
- Close contact with infected individual
- Late winter / early spring
- Crowded living conditions (schools, military barracks)
- Caregiver/parent of school-age child
Pathophysiology
S. pyogenes (Lancefield group A) adheres to pharyngeal epithelium via M protein, lipoteichoic acid, and fibronectin-binding proteins. Streptolysins and pyrogenic exotoxins cause local inflammation and systemic symptoms. Suppurative complications (peritonsillar abscess, otitis) arise from contiguous spread. Nonsuppurative sequelae (acute rheumatic fever, post-streptococcal glomerulonephritis) reflect immune-mediated cross-reactivity.
Clinical presentation
Symptoms
- Sudden onset sore throat, painful swallowing
- Fever ≥38°C (100.4°F)
- Headache, malaise
- Nausea, vomiting, abdominal pain (especially children)
- ABSENCE of cough, rhinorrhea, conjunctivitis, hoarseness — strongly suggests GAS over viral
Signs / physical exam
- Tonsillopharyngeal erythema with exudates
- Tender anterior cervical lymphadenopathy
- Palatal petechiae (uvular or soft palate)
- Scarlatiniform rash (sandpaper-like), strawberry tongue, circumoral pallor → scarlet fever
- Absence of viral features
Classic findings
Modified Centor (McIsaac) score components: fever >38, tonsillar exudate, tender anterior cervical adenopathy, absence of cough, age 3-14 (+1) or 15-44 (0) or ≥45 (-1).
Differential diagnosis
- Viral pharyngitis (adenovirus, rhinovirus, coronavirus) — Cough, rhinorrhea, conjunctivitis, hoarseness, viral exanthem — argue AGAINST GAS; supportive care
- Infectious mononucleosis (EBV) — Adolescent/young adult with fatigue, posterior cervical lymphadenopathy, palatal petechiae, splenomegaly, atypical lymphocytes; heterophile (Monospot) or EBV serology; rash develops in ~90% if amoxicillin given
- Acute HIV (seroconversion) — Sore throat, fever, lymphadenopathy, mucocutaneous ulcers, rash; HIV RNA or 4th-gen antibody/antigen test
- Gonococcal pharyngitis — Often asymptomatic; risk factors (oral sex, MSM); NAAT
- Peritonsillar abscess — Trismus, deviated uvula, hot-potato voice; needs drainage
- Retropharyngeal abscess — Neck stiffness, drooling, stridor; lateral neck XR or CT
- Epiglottitis — Drooling, tripoding, muffled voice, severe sore throat with minimal pharyngeal findings; thumbprint sign on lateral neck XR
- Diphtheria — Gray adherent pseudomembrane, unvaccinated; toxin neutralization required
- Lemierre syndrome — Persistent fever after pharyngitis, unilateral neck pain/swelling, internal jugular vein thrombophlebitis with septic pulmonary emboli; usually Fusobacterium necrophorum
- Kawasaki disease (children <5) — ≥5 days fever + 4 of 5 criteria (conjunctivitis, mucositis, rash, extremity changes, cervical lymphadenopathy); echo for coronary aneurysms
Diagnostic workup
Diagnostic criteria
IDSA 2012: confirm GAS pharyngitis with positive RADT or throat culture in symptomatic patients with clinical features suggestive of GAS (Centor ≥2-3); do not test those with overt viral features. Test of cure NOT routine.
Labs
- Rapid antigen detection test (RADT) — sensitivity ~85%, specificity >95%
- Throat culture (gold standard, ~90-95% sensitive) — required to confirm negative RADT in children/adolescents per IDSA; not necessary in adults given low GAS prevalence and minimal rheumatic fever risk
- Do NOT test asymptomatic patients (high carriage rate, false positives)
- Do NOT test patients with clear viral features (cough, coryza, conjunctivitis, hoarseness)
- ASO and anti-DNase B titers — for documenting prior GAS infection in rheumatic fever evaluation, not acute diagnosis
- Heterophile (Monospot) or EBV-specific serology if mononucleosis suspected
Imaging
- Not required for uncomplicated GAS pharyngitis
- Lateral neck XR or CT if epiglottitis, retropharyngeal abscess, or deep neck infection suspected
Diagnostic algorithm
| Modified Centor Criterion | Points |
|---|---|
| Fever >38°C (100.4°F) | +1 |
| Absence of cough | +1 |
| Tender anterior cervical lymphadenopathy | +1 |
| Tonsillar exudate or swelling | +1 |
| Age 3-14 years | +1 |
| Age 15-44 years | 0 |
| Age ≥45 years | -1 |
| Score 0-1: no testing, no antibiotic | — |
| Score 2-3: RADT; treat if positive | — |
| Score 4-5: RADT (some empiric treatment); culture if RADT negative in children | — |
Treatment
First-line
- Penicillin V 500 mg PO BID-TID × 10 days (adults) OR amoxicillin 50 mg/kg/day (max 1000 mg) once daily × 10 days (children) — narrow-spectrum, low cost, no documented resistance
- Penicillin G benzathine 1.2 million units IM × 1 (adults; 600,000 units if <27 kg) — single-dose option, ensures adherence
- Supportive care: acetaminophen or NSAIDs, saltwater gargles, hydration
- Treatment within 9 days of symptom onset prevents acute rheumatic fever; symptomatic improvement within 24-48 h
- Return to school/work after 12-24 h of antibiotic therapy and afebrile
Second-line / adjunct
- Penicillin allergy (non-anaphylactic): cephalexin 500 mg BID × 10 days, cefadroxil, or cefuroxime
- Severe penicillin allergy: azithromycin × 5 days OR clindamycin × 10 days (check local macrolide resistance; rising in US ~5-15%)
- Recurrent symptomatic GAS: confirm true infection (not carrier with intercurrent viral illness); consider clindamycin or amox-clav for re-treatment
- Tonsillectomy considered for ≥7 episodes/year, ≥5/year × 2 years, or ≥3/year × 3 years (Paradise criteria) plus documentation in each
Complications
- Suppurative: peritonsillar abscess, otitis media, sinusitis, retropharyngeal abscess, cervical lymphadenitis, Lemierre syndrome
- Nonsuppurative — acute rheumatic fever (peaks 2-4 weeks after pharyngitis; PREVENTABLE by antibiotic treatment within 9 days)
- Nonsuppurative — post-streptococcal glomerulonephritis (1-2 weeks after; NOT prevented by antibiotics; hematuria, edema, hypertension, low complement)
- Scarlet fever (erythrogenic toxin)
- Toxic shock syndrome and necrotizing fasciitis (rare, severe invasive disease)
- PANDAS — pediatric autoimmune neuropsychiatric disorder (controversial)
PANCE pearls
- Cough, coryza, conjunctivitis, hoarseness, oral ulcers → VIRAL. Do not test or treat for strep.
- Centor/McIsaac score guides testing: ≥3 → RADT; <3 → no test, no antibiotic.
- Amoxicillin given to mono produces a non-IgE-mediated maculopapular rash in 80-90% of patients — not a true penicillin allergy.
- Antibiotics prevent acute rheumatic fever but NOT post-streptococcal glomerulonephritis.
- No documented GAS resistance to penicillin — penicillin remains first-line; macrolide resistance rising.
- Test-of-cure not recommended unless symptomatic recurrence or prior rheumatic fever.
References
- IDSA 2012 — Shulman ST et al. Clinical Practice Guideline for the Diagnosis and Management of Group A Streptococcal Pharyngitis (Update). Clin Infect Dis 2012;55(10):e86-e102
- AAP Red Book 2024 — American Academy of Pediatrics. Group A Streptococcal Infections. In: Red Book 2024
- AHA — Gerber MA et al. Prevention of Rheumatic Fever and Diagnosis and Treatment of Acute Streptococcal Pharyngitis. Circulation 2009;119(11):1541-1551
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