🦠 Viral vs Bacterial Pharyngitis Differential Simulator

Patient Presents With Sore Throat

Common complaint, mostly self-limited, occasionally bacterial.

• ~12M: Annual US visits (primary care encounters/yr)
• 85–90%: Viral cause share (of all sore throat cases)
• 5–15%: Group A strep share (bacterial cases, adults)
• 5–15 yrs: Peak strep age (school-age incidence peak)

Why differentiate viral from bacterial

Guides testing, antibiotic use, and complication risk.

Typical presentation

Sore throat, odynophagia, variable fever and malaise.

Symptom Checklist — Six Clinical Signs

Toggle signs on or off to update the model live.

• 4: Centor criteria items (classic prediction rule)
• ~50–60%: Exudate sensitivity (for GAS pharyngitis)
• 3: Viral coryza signs tracked (cough, rhinorrhea, conjunctivitis)
• +1 pt: Node tenderness weight (bacterial-favoring feature)

Viral-favoring signs

Cough, rhinorrhea, conjunctivitis suggest a viral cause.

Bacterial-favoring signs

Exudate, tender nodes, fever without cough suggest strep.

Weighted Differential Score Computed Live

Each active sign adds one weighted point to its side.

• 0–6: Score range (total weighted points)
• +1: Weight per sign (each feature, either category)
• Instant: Recalculation (on every toggle change)
• Visual only: Severity influence (does not change the score)

Weighted scoring model

Each toggled sign adds one point to its category.

Live recalculation

Score updates instantly as signs are toggled.

Likely Etiology — Viral, Bacterial, or Indeterminate

Lean percentage sorts the case into three bands.

• ≥65%: Viral-leaning cutoff (lean toward viral)
• ≤35%: Bacterial-leaning cutoff (lean toward bacterial)
• 35–65%: Indeterminate band (needs further testing)
• ~85–90%: RADT sensitivity (rapid antigen detection test)

Classification bands

Viral-leaning, bacterial-leaning, or indeterminate by lean percent.

Clinical correlation

Etiology estimate still needs confirmatory testing.

Management Implication — Supportive Care vs Antibiotics

Viral gets rest and fluids; bacterial gets testing.

• 10 days: Antibiotic course (penicillin/amoxicillin standard)
• ~4000: NNT for rheumatic fever (number needed to treat)
• 5–7 days: Supportive care duration (typical viral course)
• ~60%: Overtreatment estimate (sore throats given antibiotics needlessly)

Viral management

Supportive care only — fluids, rest, analgesia.

Bacterial management

Consider rapid strep testing, then targeted antibiotics.