Background: Sinusitis, defined as inflammation of one or more of the paranasal sinuses, is characterized as acute when lasting less than 4 weeks, subacute when lasting 4 to 8 weeks, and chronic when lasting longer than 8 weeks. Recurrent sinusitis consists of 3 or more episodes of acute sinusitis per year. A noninfectious form of chronic sinusitis is termed chronic hyperplastic eosinophilic sinusitis. Viral upper respiratory tract infections frequently precede subsequent bacterial invasion of the sinuses by Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis.