Bacterial infection of the middle ear results from nasopharyngeal organisms migrating via the eustachian tube. The anatomy of the eustachian tube in younger children is immature, typically being short, straight, wide (only becoming more oblique as the child grows), meaning infection is more likely.

Sound waves enter the outer ear and travel through a narrow passageway called the ear canal, which leads to the eardrum. The eardrum vibrates from the incoming sound waves and sends these vibrations to three tiny bones in the middle ear. These bones are called the malleus, incus, and stapes