Acute otitis media: Epidemiology, Aetiology, Pathophysiology & diagnosis

Acute otitis media (AOM) is an infection involving the middle ear space and is a common complication of viral respiratory illnesses.

More than 80% of children experience at least one episode of AOM before the age of 2 years, with a peak incidence between 6 and 18 months. [ref-1]

Children with anatomical anomalies (e.g., cleft palate, cleft uvula) or immunological deficiencies encounter more AOM than their peers.

Environmental risk factors include: 
  • Childcare attendance  
  • Exposure to older siblings, 
  • exposure to tobacco smoke, 
  • absence of breastfeeding, 
  • bottle feeding in a supine position
  • dummy use. [ref-2]

A higher incidence among boys, children with a family history of AOM, and certain ethnic groups (Native Americans and Native Alaskans) suggests a genetic susceptibility.

Why Acute otitis media is more common in infants and young children than in adults?

This is because:
  • Eustachian tube is wider, shorter and more horizontal than in adults making it easier to transmit infection to the middle ear.
  • More common causes of acute otitis media: Adenoiditis, Tonsillitis, Exanthemata, and contaminated milk may enter the Eustachian tube when feeding in the supine position.
  • Lowered resistance due to: teething, Gastrointestinal troubles, Artificial feeding, and immune system not well developed.


Respiratory viruses account for most cases of otitis media and are self-limiting. 

Co-infections of the middle ear with a virus and a bacterium demonstrate the role that both play in the development of acute, suppurative otitis media.

The most common bacteria responsible for AOM are Streptococcus pneumoniae (approximately 40%), non-typable Haemophilus influenzae (25% to 30%), and Moraxella catarrhalis (10% to 15%).

Unfortunately, an aetiological diagnosis in a clinic setting is not feasible.


Under normal conditions the mucociliary action and ventilatory function of the eustachian tube clear the nasopharyngeal flora that enter the middle ear. 

However, upper respiratory viruses can infect the nasal passages, eustachian tube, and middle ear, causing inflammation and impairing these processes. This may then contribute to the development of AOM. [ref-3]

A middle ear effusion develops, and nasopharyngeal bacteria contaminate the effusion. 

The middle ear effusion provides a good medium for bacterial growth, which then precipitates a suppurative, inflammatory response.

Suppuration and subsequent pressure against the tympanic membrane lead to pain and fever, which are typical symptoms of AOM.

In more severe cases, the tympanic membrane may perforate and cause a purulent otorrhoea (White thick discharhe). 

The inflammatory process may also involve the mastoid air cells. Fortunately, AOM is usually self-limiting.

Symptoms in infants and young children

More severe general constitutional symptoms than in adults. Vomiting and diarrhea may occur. 
The child cries, does not sleep, moves his/her head and pulls the ears. 


  • Diffuse congestion. 
  • Bulging and perforation occur later than in adults due to thicker drum and more obliquity of the drum, so complications are more common.

Approach to diagnosis

The key factors in the history that support the diagnosis of AOM vary depending on the age of the patient. 

In an older, verbal child they include a preceding viral respiratory illness followed by the acute onset of otalgia. 

In a pre-verbal child, the key factors should include fever or systemic symptoms indicative of otalgia such as irritability, crying, sleep disturbance, vomiting, or poor appetite. 

Pre-verbal children may tug, rub or hold the affected ear, though these symptoms are not specific to the diagnosis of AOM.

AOM occurs much less frequently in adults than in children. 
Adults typically present more quickly than children with complaints of ear pain, decreased hearing, sore throat, and otorrhoea. 

Adults have higher rates of persistent middle ear effusions or infections 2 months after initial diagnosis compared with children.

Bacteriology and treatment are similar to those for children.


Factors in the physical examination that support the diagnosis of AOM specifically include a bulging, opaque tympanic membrane. 

The tympanic membrane may appear white, yellow, pink or red.
Otoscopy appearance of a bulging, erythematous tympanic membrane and absent landmarks
Otoscopy appearance of a bulging, erythematous tympanic membrane and absent landmarks

In a neutral position, a normal tympanic membrane appears draped over the umbo centrally and the lateral process of the malleus is visible in the anterosuperior quadrant.
tympanic membrane otoscopy
Normal tympanic membrane, appearing draped over the umbo centrally, and the lateral process of the malleus in the anterosuperior quadrant. LM = lateral process of the malleus; I = incus; U = umbo; LR = light reflex; A = annulus of tympanic membrane; PI = posterior inferior quadrant

In addition, a light reflex should be visible in the anteroinferior quadrant. 

When AOM develops, the tympanic membrane will bulge (bagel sign), obscuring these landmarks and splaying or attenuating the light reflex.

Purulent middle ear effusion and tympanic membrane with a loss of landmarks and characteristic bagel or doughnut appearance

As such, examination of the external auditory canal and visualisation of the tympanic membrane are the accepted standard for the diagnosis of AOM.

On occasion, cerumen in the external auditory canal may interfere with visualisation of the tympanic membrane. 

Every effort should be made to clear the cerumen from the external auditory canal. If the tympanic membrane cannot be visualised, then a judgment must be made regarding the appropriate management of the patient.


Usually no tests are necessary: AOM is a clinical diagnosis.

Additional tests might include pneumatic otoscopy or tympanometry to confirm the presence of an effusion.

Tympanocentesis and bacterial culture of aspirated middle ear fluid are the means of making an aetiological diagnosis. 

However, tympanocentesis is technically difficult to perform and may require a referral to an otolaryngologist; additionally, the patient's condition is likely to have improved before culture results are available. 

Therefore, it is usually only performed in patients with persistent AOM unresponsive to antibiotics, or to provide immediate relief of severe pain.

Differential diagnosis

Criteria of diagnosis of Acute (suppurative) otitis media

The American Academy of Pediatrics criteria for AOM:

  • Moderate to severe bulging of the tympanic membrane, OR
  • Mild bulging of the tympanic membrane AND recent onset of ear pain or intense erythema of the tympanic membrane.
These criteria reflect a more stringent approach than those offered in other guidelines where the mere presence of a middle ear effusion may be sufficient to diagnose the condition. 

Research has shown that many children meet less stringent criteria for AOM frequently during the course of a common cold, even though they may not seek care from their physician.
Acute otitis media: Epidemiology, Aetiology, Pathophysiology & diagnosis
Dr.Tamer Mobarak


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