Differentiating Viral vs. Bacterial Upper Respiratory Tract Infection (URTI)

1. Etiology at a Glance

• ROSEN's Emergency Medicine, p. 957

2. Clinical Features

Viral URTIs - Classic Symptoms

• Gradual onset of sore/scratchy throat (often the first symptom)
• Rhinorrhea (clear initially, may become discolored but this does NOT indicate bacterial superinfection)
• Nasal congestion and sneezing
• Cough (develops later, may persist weeks)
• Hoarseness (suggests laryngeal involvement)
• Conjunctivitis (particularly with adenovirus - "pharyngoconjunctival fever")
• Low-grade or absent fever
• General malaise
• Symptoms appear as a cluster spread over several days
• Goldman-Cecil Medicine, p. 3503

Bacterial URTIs - Classic Symptoms (GAS Pharyngitis)

• Rapid/abrupt onset of severe sore throat
• Odynophagia (pain on swallowing)
• High fever (>38°C), chills
• Tonsillar swelling with exudates (white/yellow patches)
• Tender anterior cervical lymphadenopathy
• Foul breath (halitosis)
• Headache, malaise, anorexia
• Palatal petechiae (pathognomonic when present)
• Scarlatiniform rash in scarlet fever
• ABSENCE of cough - important distinguishing feature
• ABSENCE of rhinorrhea, hoarseness, conjunctivitis - these suggest viral etiology
• Goldman-Cecil Medicine, p. 4188-4189

3. The Key Clinical Rule: ABSENCE of Cough

Cough present = more likely viral. Absence of cough = points toward bacterial (GAS).

4. Modified Centor Score (McIsaac Score)

• Score 0-1: No testing, no antibiotics (almost certainly viral)
• Score 2-3: Rapid antigen test recommended; treat if positive
• Score 4-5: High suspicion; empiric antibiotics reasonable, confirm with culture if test negative
• ROSEN's Emergency Medicine, Table 19.1

5. Feature-by-Feature Comparison Table

6. Special Clues for Specific Infections

• Infectious mononucleosis (EBV): Exudative pharyngitis + posterior cervical lymphadenopathy + splenomegaly + atypical lymphocytes - can mimic bacterial pharyngitis but is viral
• Adenovirus: Pharyngoconjunctival fever (pharyngitis + conjunctivitis together strongly suggests adenovirus)
• Herpangina (Coxsackievirus): Small vesicles/ulcers on soft palate and tonsillar pillars - distinctly viral
• Diphtheria (C. diphtheriae): Grayish-green pseudomembrane tightly adherent to mucosa, friable - a dangerous bacterial cause. Consider in unvaccinated patients.
• Fusobacterium: Young adults (15-45 yrs) with severe GAS-like symptoms but culture-negative for strep; risk of Lemierre syndrome
• ROSEN's Emergency Medicine, p. 957-958

7. Investigations

• A systematic review (PMID: 39359102) confirmed that point-of-care rapid antigen tests are useful for distinguishing viral from bacterial acute respiratory infections.
• The Goldman-Cecil Medicine notes: "A rapid test for streptococcal pharyngitis may be useful in patients with pharyngeal exudates, swollen cervical lymph nodes, feverishness, and absence of cough."

8. Pitfalls to Avoid

1. Discolored nasal discharge does NOT equal bacterial sinusitis - color change is common during viral colds and does not mandate antibiotics.
2. Exudates are not exclusive to bacteria - EBV and adenovirus can produce pharyngeal exudates.
3. Sinusitis features suggesting bacterial superinfection: Symptoms persisting >10 days WITHOUT improvement + unilateral maxillary pain + purulent discharge.
4. Antibiotic overuse is common in URTIs - most are viral and resolve spontaneously within 7-10 days.

Summary

• Cough/rhinorrhea/hoarseness/conjunctivitis = viral
• Abrupt onset + high fever + tonsillar exudates + tender anterior cervical nodes + NO cough = bacterial (GAS)
• Use the Modified Centor (McIsaac) Score to guide testing and antibiotic decisions
• Confirm with a rapid strep test or throat culture when score is 2 or more