Medical Health Encyclopedia

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.
• Moraxella catarrhalis is responsible for 10 - 20% of infections.
• Other bacteria include  Streptococcus pyogenes and Staphylococcus aureus.

About 15% of AOM-causing bacteria are now believed to be resistant to the first-choice antibiotics.

Viruses. Rhinovirus is a common virus which 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 such viruses play a greater role in ear infectins than previously believed. The theory rests on the significantly lower rates of ear infections in children who have received flu vaccines.

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Allergies. Allergies can cause inflammation in the airways, and contribute to ear infections.

Inborn Conditions that Predispose a Child to Middle Ear Infections

Genetic Factors. Several studies suggest that multiple genetic factors may make a child more susceptible to acute otitis media.

• Genetic susceptibility to certain bacteria may result in development of persistent and recurrent acute otitis media.
• Abnormalities in genes that affect the defense systems (cilia and mucus production) and the anatomy of the skull and passages would also increase the risk for ear infections.
• Abnormalities in genes that regulate a powerful immune factor called interleukin 1 have been identified in some patients with recurrent acute otitis media who did not have any allergic disorders. Interleukin-1 plays a major role in producing inflammation in tissues and cells during heightened immune activity. Abnormalities in interleukin production may possibly result in a persistent inflammatory response.