Several. The foul odor is due to a combination of factors, not the least of which is stagnant pus in a cavity with decay due to the inflammation. Investigators at the univ. Of va showed many years ago that anaerobic bacteria may be causing sinusitis, and these organisms produce fatty acids and other materials which may be malodorous. Create drainage, irrigate, use antibiotics, treat allergies.
Infections. Yes and no. It depends. Viral infections are also a common source of sinus infections. They are no all bacterial infections.