What is the most likely diagnosis and recommended treatment for an adult who develops new unilateral ear pain shortly after an upper respiratory tract infection?

Unilateral Ear Pain After URTI in Adults

The most likely diagnosis is acute otitis media (AOM), and first-line treatment is high-dose amoxicillin-clavulanate (1.75-4 g amoxicillin/250 mg clavulanate daily) with systemic analgesics for pain control. 1

Most Likely Diagnosis

Acute otitis media is the primary diagnosis to consider when unilateral ear pain develops following an upper respiratory tract infection in adults. 2, 1

• AOM occurs as a bacterial superinfection complicating viral URTI, with rates of 37% in the peak age groups, though adults are also affected 2
• The pathophysiology involves Eustachian tube dysfunction during viral URI, allowing nasopharyngeal bacteria to ascend into the middle ear 3, 4
• The three primary bacterial pathogens are Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis 2, 1, 4

Key Diagnostic Features

• Bacterial superinfection risk is greatest if URI symptoms persist beyond 10 days or worsen after 5-7 days 2
• Clinical diagnosis requires moderate-to-severe bulging of the tympanic membrane, or mild bulging with recent onset ear pain, or intense erythema of the tympanic membrane 2
• Pneumatic otoscopy is the primary diagnostic method to confirm middle ear effusion 5
• Tympanometry can confirm diagnosis when otoscopy is uncertain 5

Common Pitfall: Do not assume ear pain during URI is simply referred pain from pharyngitis—always examine the tympanic membrane to exclude AOM 1

First-Line Treatment Algorithm

Step 1: Immediate Pain Management

All patients require systemic analgesics, especially during the first 24 hours. 1

• Acetaminophen or ibuprofen should be offered to all patients 1
• Topical analgesics may reduce ear pain within 10-30 minutes, though evidence quality is low 1

Step 2: Antibiotic Selection

For confirmed AOM in adults without penicillin allergy, amoxicillin-clavulanate is the first-line systemic antibiotic. 1

Standard Dosing:

• Mild disease without recent antibiotic exposure: 1.75 g amoxicillin/250 mg clavulanate per day 1
• Recent antibiotic use or moderate disease: 4 g amoxicillin/250 mg clavulanate per day 1

Rationale for Amoxicillin-Clavulanate:

• Covers S. pneumoniae (including penicillin-intermediate strains), β-lactamase-producing H. influenzae (20-30% of strains), and β-lactamase-producing M. catarrhalis (50-70% of strains) 2, 1
• Predicted clinical efficacy of 90-92% in adults 1
• The β-lactamase inhibitor is essential because 20-30% of H. influenzae and 50-70% of M. catarrhalis strains produce β-lactamase 2

Step 3: Penicillin-Allergic Patients

For confirmed penicillin allergy, respiratory fluoroquinolones (levofloxacin or moxifloxacin) are the preferred alternatives. 1

• These provide 90-92% clinical efficacy, equivalent to amoxicillin-clavulanate 1
• Azithromycin is inferior with only 77-81% predicted efficacy and 20-25% bacteriologic failure rates 1

Critical Pitfall: Do not use azithromycin as first-line therapy—it has inadequate coverage against resistant S. pneumoniae and substantially lower efficacy than amoxicillin-clavulanate or fluoroquinolones 1

Monitoring and Treatment Failure

Expected Response Timeline

• Clinical improvement should occur within 48-72 hours of initiating appropriate antibiotic therapy 2, 1
• Middle ear effusion may persist for weeks to months after AOM symptoms resolve, even when sterile 2

Reassessment Protocol

If no improvement by 48-72 hours, reassess to confirm AOM and exclude other diagnoses. 1

• For confirmed treatment failure, switch to a different antibiotic class rather than increasing dose 1
• Do not continue the same antibiotic beyond 72 hours without improvement 1

Common Pitfall: Persistent middle ear effusion after successful AOM treatment does not require continued antibiotics—this represents otitis media with effusion (OME), which is managed with watchful waiting 5

Alternative Diagnoses to Consider

While AOM is most likely, consider these alternatives if presentation is atypical:

Otitis Externa

• More common than AOM in adults (10% lifetime incidence) 1
• Presents with ear canal pain worsened by tragal pressure or pinna manipulation 1
• Requires topical antibiotic therapy, not systemic antibiotics 1

Otitis Media with Effusion (OME)

• Middle ear fluid without acute infection symptoms 2, 5
• Managed with watchful waiting for 3 months, not antibiotics 5
• Antihistamines, decongestants, and systemic antibiotics are ineffective 5

When to Avoid Antibiotics

Do not prescribe systemic antibiotics for uncomplicated otitis externa—this increases antibiotic resistance without benefit. 1

• Topical antibiotics deliver 100-1000 times higher concentration than systemic therapy 1
• Systemic antibiotics for otitis externa are only indicated when infection extends beyond the ear canal 1

Special Populations Requiring Modified Approach

• Diabetic or immunocompromised patients: Higher risk for necrotizing otitis externa and otomycosis; may require systemic antibiotics in addition to topical therapy 1
• Prior radiotherapy: May require systemic antimicrobials 1
• Non-intact tympanic membrane or tympanostomy tubes: Requires special consideration for medication choice 1