Causes:

Infections

Bacteria. Certain bacteria are the primary causes of acute otitis media (AOM). They are detected in about 60% of cases. The bacteria most commonly causing ear infections are:

• Streptococcus pneumoniae (also called S. pneumoniae or pneumococcus) is the most common bacterial cause of acute otitis media, causing about 40 - 80% of cases in the U.S.
• Haemophilus influenzae, the next most common culprit, is responsible for 20 - 30% of acute infections.
• Moraxellacatarrhalis is responsible for 10 - 20% of infections.
• Other bacteria include Streptococcus pyogenes and Staphylococcus aureus.

Viruses. Rhinovirus is a common virus that causes a cold and plays a leading role in the development of ear infections. It is not the direct infecting organism, however. But other viruses, such as respiratory syncytial virus (RSV, a virus responsible for childhood respiratory infections) and influenza (flu), may be the actual causes of some ear infections. Increasing evidence suggests that both viruses and bacteria play a role in ear infections. Viruses can increase middle ear inflammation and interfere with antibiotics’ efficacy in treating bacterial-causes ear infections. HIV or other immunocompromised states also increase the risk for ear infections.

Acute otitis media (middle ear infection) is usually due to a combination of factors that increase susceptibility to infections by specific organisms in the middle ear. The infection typically evolves as follows:

• The primary setting for ear infections is in a child's Eustachian tube, which runs from the middle ear to the nose and upper throat. The Eustachian tube is shorter and smaller in children than adults, and therefore more vulnerable to blockage. It is also more horizontal in younger children and therefore does not drain as well.
• Changes in middle ear pressure occur in about two-thirds of children with colds. Colds and respiratory infections are caused by viruses, such as the rhinovirus. Viruses play an important role in many ear infections, and can set the scene for a bacterial infection.
• However, many bacteria normally thrive in the passages of the nose and throat. Most are not harmful. In fact, some can even block harmful bacteria from getting out of control. An additional defense system in the airways, such as mucus, prevents the harmful bacteria from spreading and infecting deeper passages, such as those in the ear.
• If a cold does occur, the virus can cause the membranes along the walls of the inner passages to swell and obstruct the airways. If this inflammation blocks the narrow Eustachian tube, the middle ear may not drain properly. Fluid builds up. The defense systems described above become inefficient, and the fluid becomes a breeding ground for bacteria and subsequent infection.

Respiratory viruses may also contribute directly to the infection. Allergens can also produce inflammation and blockage in the Eustachian tube, which creates an environment favorable to bacteria.

The rise in ear infections has paralleled the increasing incidences of other upper and lower airway disorders such as asthma, allergies, and sinusitis. For example, the same bacteria are often responsible for both ear infections and sinusitis. In one study, 38% of children with ear infections also had sinusitis, and other studies have reported that nearly half of children with OME have concurrent sinusitis. Data indicate that nearly a third of infants and toddlers with upper respiratory infections go on to develop acute otitis media.

Anatomic Abnormalities

Medical or Physical Conditions that Affect the Middle Ear. Any medical or physical condition that reduces the ear's defense system can increase the risk for ear infections. Children with shorter than normal and relatively horizontal Eustachian tubes are at particular risk for initial and recurrent infections. Inborn structural abnormalities, such as cleft palate, increase risk. Genetic conditions, such as Kartagener's syndrome in which the cilia (hair-like structures) in the ear are immobile and cause fluid build up, also increase the risk. Children with Down syndrome or Fetal Alcohol Syndrome may also be at increased risk due to anatomical abnormalities.

Otitis media with effusion (OME) may occur spontaneously following an episode of acute otitis media. Susceptibility to OME may also be due to an abnormal or malfunctioning Eustachian tube that causes a negative pressure in the middle ear, which allows fluid to leak in through capillaries.