The answer to this question would be: Place the baby in an upright position when giving a bottle.
Otitis media is an inflammation of the middle part of the ear. This part normally can't be reached from the external ear because there is a tympanic membrane that acts as a barrier. But it can be reached from the nasopharynx since it was connected to the ear by eustachian tube.
Putting the baby in an upright position will lower the risk of fluid got stuck inside the middle ear.