How can I differentiate between viral and bacterial causes of acute otitis media in my patients?

Distinguishing viral from bacterial causes of acute otitis media (AOM) clinically is challenging because symptoms often overlap. However, certain features can guide differentiation:

• Symptom onset and severity: Bacterial AOM typically presents with rapid onset of moderate to severe ear pain, fever, and systemic symptoms, whereas viral AOM may have milder symptoms and often improves without antibiotics.
• Response to antibiotics: Improvement within 2–3 days of antibiotic treatment suggests bacterial infection; lack of improvement may indicate viral infection or other causes.
• Presence of complications or red flag symptoms: Severe systemic infection signs, persistent high fever, or complications such as mastoiditis suggest bacterial etiology requiring urgent specialist assessment.
• Clinical examination: Bulging, erythematous tympanic membrane with middle ear effusion is common in bacterial AOM, but viral infections can also cause inflammation; persistent effusion without acute inflammation suggests otitis media with effusion rather than acute infection.

Routine microbiological testing is not recommended in primary care; diagnosis relies on clinical assessment and symptom progression. If symptoms persist or worsen despite antibiotics, reassessment is necessary to exclude other causes or resistant bacterial infection.

In summary, differentiation is primarily clinical, based on symptom severity, progression, and response to treatment, with bacterial AOM more likely in cases with rapid onset, severe symptoms, and improvement after antibiotics, while viral AOM often resolves without antibiotics.

References: NICE CKS