Is sinusitis an infectious disease?

Yes: Most commonly sinusitis is caused by a bacterium called pneumococcus or one called nontypable haemophilus influenza or one called moraxalla. These are infectious but not contagious.

Sometimes: Not always. Sinusitis just means inflammation of the sinus cavities. The symptoms can be nasal congestion, pressure or headaches over the sinuses, tooth pain, nasal discharge (clear or purulent), postnasal drip, sore throat, fevers, fatigue or bad breath. It can be caused by anything that inflames the sinuses, like viruses, bacteria, allergies, smoke, fumes, etc., thus we treat the cause.

Sometimes: Sinusitis can be caused by viral or bacterial infection which would be infectious diseases. Sinusitis can occur from non- infectious causes as well such as allergies/hay fever and wegener's granulomatosis as examples.

Yes: Yes Sinusitis is an infectious disease and may be caused by viruses or Bacteria and rarely by fungi