Q: Mike: You’ve said the common cold is caused by a virus. I get ear infections when I recover from a cold, and the doctor gives me antibiotics for it. Why?
A: Dean Edell, M.D.: Good question. The cold virus causes your membranes to swell, and in some people the swelling closes off the Eustachian tube, closes off sinus cavities, and then bacteria gets in there.
So the ear infection or the sinus infection itself is not usually caused by a virus, but it can be appropriate to treat it with antibiotics. There are more and more questions about that, though.