The middle ear is connected to the back of the nose via a small canal called the eustachian tube. Bacteria can make their way into the middle ear via this canal where they are usually flushed out through the eustachian tube. Both bacteria and virus can infect the middle ear.
A blockage in the canal (usually due to a cold/flu), or when it does not function properly, can lead to germs getting trapped in the middle ear, causing an ear infection.
Children are predisposed to suffer from acute otitis media because of the anatomy and function of their ears and eustachian tube.
Children are prone to ear infections because their eustachian canal is smaller and more horizontal. They tend to get more ear infections between 6 to 24 months. They are also more prone to upper respiratory tract infections such as colds and flus.
An ear infection, in itself, is not contagious but the upper respiratory viruses that cause the infection can spread amongst children. Therefore, children in day care are more prone to ear infections. Children who use pacifiers are also at risk.
Other risks factors include immature immune systems and factors that can cause the eustachian canal to be blocked are allergies, acid reflux, or environmental irritants like tobacco smoke.