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Infection: Ear infections can start with a bacterial or viral infection (such as those causing common cold). In such cases, the middle ear becomes inflamed from the infection, and fluid builds up behind the eardrum. Bacteria cause about 65-75% of all ear infections. The most common types are Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis. Viruses that may lead to ear infections include the respiratory syncytial virus (RSV), the most frequent type found, followed by influenza (flu) viruses. Eustachian tube problems: Ear infections also may be associated with problems such as swelling within the eustachian tubes, the narrow passageways that connect the middle ear to the throat. Normally these tubes equalize pressure inside and outside the ear. But a child's eustachian tubes are narrower and shorter than those of an adult. This makes it easier for fluid to get trapped in the middle ear when the eustachian tubes dysfunction or become blocked during a cold. This provides a perfect breeding ground for infection. Also, just as the mucus in the nose gets thicker and harder to expel, fluid within the ear can also become thick and difficult to drain. Adenoids (tonsils): Another factor in ear infections is swelling of the adenoids (tonsils). These are tissues located in the upper throat near where the eustachian tubes connect. Adenoids contain lymphocytes, or types of white blood cells that normally fight infection. But sometimes the adenoids themselves get infected or enlarged, blocking the eustachian tubes. Infection in the adenoids can also spread to the eustachian tubes, causing ear infections. Immune function: Children also do not have fully developed immune systems, so it is easier for them to develop many illnesses, including ear infections.
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