What is the best next step in management of a 4‑month‑old infant girl with unilateral purulent middle‑ear effusion and reduced tympanic‑membrane mobility on pneumatic otoscopy, no fever, well‑breastfed, no pacifier use, and no recent infections?

Management of 4-Month-Old with Unilateral Purulent Middle Ear Effusion

This infant requires immediate antibiotic treatment with amoxicillin, not observation, because the presence of purulent effusion with decreased tympanic membrane mobility represents acute otitis media (AOM), not otitis media with effusion (OME), and infants under 6 months of age are a specific population requiring immediate antimicrobial therapy.

Critical Diagnostic Distinction

The key to this case is recognizing that purulent effusion distinguishes AOM from OME:

• Acute otitis media is characterized by rapid onset of middle ear inflammation with purulent effusion, bulging tympanic membrane, and decreased mobility 1
• Otitis media with effusion presents with middle ear fluid but WITHOUT signs of acute infection—the tympanic membrane is cloudy with impaired mobility but lacks the purulent character 1
• The presence of purulent effusion in this case definitively indicates AOM, not OME 1

Age-Specific Treatment Algorithm

For infants under 6 months of age with AOM, immediate antibiotic therapy is mandated 2:

• Children under 6 months represent a high-risk population requiring immediate treatment regardless of symptom severity 2
• The absence of fever does NOT change this recommendation—age alone determines the need for immediate antibiotics in this population 2
• Watchful waiting (observation for 48-72 hours) is appropriate only for older children (≥6 months) with non-severe symptoms 2, 3

First-Line Antibiotic Selection

Amoxicillin is the preferred first-line agent 2:

• Standard-dose amoxicillin should be initiated for uncomplicated AOM in this age group 2
• Amoxicillin-clavulanate is reserved for specific situations: recent antibiotic exposure (within 30 days), concurrent purulent conjunctivitis, or treatment failure after 48-72 hours 2, 3
• This infant has no recent history of infections, making amoxicillin-clavulanate unnecessary and exposing her to increased risk of adverse effects without added benefit 2

Why Other Options Are Incorrect

Observation with 48-hour follow-up (Option C) is inappropriate because:

• Watchful waiting applies only to children ≥6 months of age with non-severe AOM 2
• This 4-month-old falls below the age threshold for observation 2
• The purulent nature of the effusion confirms active infection requiring treatment 1

ENT referral for tympanostomy tubes (Option D) is premature because:

• Tympanostomy tubes are indicated for chronic OME persisting ≥4 months with documented hearing loss, NOT for acute infection 4, 5
• This represents a first episode of AOM without recurrence or chronicity 4
• Surgical intervention would only be considered after recurrent AOM (≥3 episodes in 6 months or ≥4 in 12 months) or persistent OME after resolution of acute infection 5, 6

Common Pitfall to Avoid

The most critical error would be misdiagnosing this as OME and withholding antibiotics:

• OME guidelines emphasize watchful waiting and avoiding antibiotics because OME is NOT an acute infection 4, 5, 6
• However, those guidelines explicitly state they do NOT apply to AOM 1
• The presence of purulent effusion is the distinguishing feature that mandates active treatment 1

Answer: A. Start amoxicillin treatment