It is an infection and inflammation of the middle ear. Usually otitis media is acute but it can become chronic. Otitis media is more common in bottle-fed infants, especially with ‘bottle-propping’, when milk can run into the eustachian tube (the narrow tube connecting the middle ear to the pharynx).
Acute otitis media is caused by viruses and bacteria that reach the middle ear from the pharynx via the eustachian tube. The important bacteria are Pneumococcus, Haemophilus, Moroxella and Streptococcus. With a common cold, swelling of the mucosa may block the eustachian tube and cause a build up of fluid in the middle ear where bacteria can thrive.