May 17, 2013 Bacteria are the most common direct cause of acute
sinusitis. (Other organisms might be the infecting cause in less
common cases.) The ability of bacteria or other organisms to
infect the sinuses, however, must first be set up by conditions
that create a favorable environment in the sinus cavities.
Sinusitis is most often an acute condition, which is self-
limiting and treatable. In some cases, however, the inflammation
in the sinuses is lasting, or is chronic to begin with. The
causes for such chronic sinusitis cases are sometimes unclear.
Upper Respiratory Infections The typical process leading to
acute sinusitis starts with a cold virus. Over 85% of people
with colds have inflamed sinuses. These inflammations are
typically brief and mild, however, and very few people with
colds develop true sinusitis. Instead, colds and flu set the
stage by causing inflammation and congestion in the nasal
passages (called rhinitis), leading to obstruction in the
sinuses. This creates a hospitable environment fo