A Middle Ear infection can cause a Conductive hearing called Otitis Media.
The constriction of the movement of the Tympanic Membrand and/or ossicles frequently causes a socially significant conductive hearing loss.
By socially significant, I mean it interferes with social interaction, and for children it retards the development of language.
An infection in the middle ear is called Otitis Media.
If it persists, the fluid in the middle ear cavity can become laden with dead white corpuscles. It then becomes viscous, and interferes with hearing even more severely. It can actually erode the ossicles and break into the inner ear which would be potententally a major disaster.
To make matters worse, the germs become lodged in the porous bone surrounding the middle ear cavity. Here, conditions for germ survival are paramount.
NOTES: Here is some interesting information on middle ear infections.