Can fungus cause sinusitis?

Yes.: Fungus infection is one (of several) cause of chronic sinusitis.

Yes: This is not common in USA. Usually it is a diabetic (mucormycosis) or a person with serious disease involving deficient immunity. The use of antibiotics makes it more likely. Antibiotics are seldom useful for sinus congestion but frequently prescribed by physicians who should know better.

It can but uncommon: Fungus infections can cause sinusitis but it is rather rare.Most of the sinus infections are caused by Viruses and Bacteria It happens mostly in immune compromised individuals.Most common pathogens are Aspergillus and mucor species