One additional note: As you can see from my credentials, I am not a neurologist. I'm glad to offer you my best guidance and opinion, but you might consider posting your question on the Neurology Forum as well, wher it can be considered by a neurologist from the Cleveland Clinic.
Here is a reference you might find helpful in this regard.
http://pedsinreview.aappublications.org/cgi/content/extract/27/5/e42
Yes, repeated infections can have an impact on hearing. Your son's development of speech/language is definitiely delayed, and this warants evaluation by a Speech/Language therapist. But an audiological evaluation is crucial, because it is possible that the delay in speech is secondary to hearing loss.
Would you describe in a little more detail the activity you refer to as seizure activity?