Judith mentions infections here:

http://www.medscape.com/viewarticle/421033
Judith Shannon Lynch, MS, MA, APRN, FAANP

"Chronic nasal congestion is one of the most common complaints seen in
primary care settings. Etiologies include bacterial and viral
infections, allergy, abuse of decongestant nasal sprays, certain
hormonal disorders (pregnancy and hypothyroid states), various anatomic
abnormalities (deviated septum), and rarely neoplasia. Often symptoms
are so similar that there is a real possibility of error in diagnosis
and, thus, inappropriate treatment.

The most common causes of chronic nasal congestion are allergic
rhinitis, from environmental allergens or irritants, and chronic
rhinosinusitis. Chronic rhinosinusitis is defined as a sinus infection
of greater than 12 weeks' duration that includes 2 or more major sinus
symptoms or at least 1 major and 2 minor symptoms.[1] "