The most common cause of sinus issues in the population is the colonization of a virus in the nasopharynx and sinus cavities. However, chronic sinus problems can be caused by the colonization of bacteria in these regions as well. Many different types of bacteria live in the nasal passages and pharynx and do not usually cause any problems, similar to the flora that lives in the digestive tract. However, bacteria can accidentally become deposited in the sinus cavities through coughing, sneezing, or direct invasion due to conditions that are favorable to its growth.
Inflammation of the sinus canals from environmental irritants, a weakened immune system, ciliary malfunction, and other mechanisms can provide bacteria with a favorable environment to colonize further. Types of bacteria known to cause sinus problems in some individuals include Hemophilus influenzae, Streptococcus pneumoniae, Streptococcus pyogenes, anaerobes, Moraxella catarrhalis, Pseudomonas aeruginosa, Klebsiella pneumoniae, Escherichia coli, Enterobacter species, Proteus mirabilis, and Staphylococcus aureus.