What causes acute sinusitis?

Updated: Apr 22, 2020
  • Author: Ted L Tewfik, MD; Chief Editor: Arlen D Meyers, MD, MBA  more...
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The bacteria most commonly involved in acute sinusitis are part of the normal nasal flora. These bacteria can become sinus pathogens when they are deposited into the sinuses by sneezing, coughing, or direct invasion under conditions that optimize their growth. The most common bacterial pathogens in acute sinusitis are Streptococcus pneumoniae (30-40%), Haemophilus influenzae (20-30%), and Moraxella catarrhalis (12-20%). Staphylococcus aureus and Streptococcus pyogenes are isolated in rare cases. Sixty-six percent of patients with acute sinusitis grow at least 1 pathogenic bacterial species on sinus aspirates, while 26-30% percent of patients have multiple predominant bacterial species.

Anaerobic organisms have been found in fewer than 10% of patients with acute bacterial sinusitis, despite the ample environment available for their growth. The exceptions are in sinusitis resulting from a dental source and in patients with chronic sinus disease, in whom anaerobic organisms are usually isolated.

Gram-negative organisms, including Pseudomonas aeruginosa (15.9%), Escherichia coli (7.6%), Proteus mirabilis (7.2%), Klebsiella pneumoniae, and Enterobacter species, predominate in nosocomial sinusitis, accounting for 60% of cases. Polymicrobial invasion is seen in 25-100% of cultures. The other pathogenic organisms found in nosocomial patients are gram-positive organisms (31%) and fungi (8.5%). Viruses are the most common trigger of acute sinusitis. Rhinovirus, influenza, and parainfluenza viruses are the primary pathogens in 3-15% of patients with acute sinusitis.

Fungal causes of sinusitis are discussed in Allergic Fungal Sinusitis and Sinusitis, Fungal.

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