What are the common bacteria and viruses present in sinusitis?

Common Bacteria and Viruses in Sinusitis

In sinusitis, the most common bacterial pathogens are Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis in acute cases, while Staphylococcus aureus and anaerobic bacteria predominate in chronic sinusitis. 1

Acute Sinusitis Pathogens

Bacterial Causes

• Primary bacterial pathogens:
  • Streptococcus pneumoniae (responsible for >50% of cases in adults) 1
  • Haemophilus influenzae (non-typeable) 1
  • Moraxella catarrhalis (especially common in children) 1

Viral Causes

• Viral infections frequently precede bacterial sinusitis, with viruses found in approximately 15% of sinus aspirates 1
• Common viral pathogens include:
  • Rhinovirus
  • Influenza virus
  • Parainfluenza virus
  • Adenovirus 1, 2

Chronic Sinusitis Pathogens

Bacterial Causes

• Primary bacterial pathogens:
  • Staphylococcus aureus (10% of cases) 1
  • Anaerobic bacteria:
    • Prevotella species (31%)
    • Anaerobic streptococci (22%)
    • Fusobacterium species (16%)
    • Peptostreptococcus species 1, 3
  • Aerobic bacteria:
    • Streptococcus species (21%)
    • Haemophilus influenzae (16%)
    • Pseudomonas aeruginosa (16%)
    • Moraxella catarrhalis (10%) 1

Fungal Causes

• Fungi are increasingly recognized in chronic sinusitis, particularly in immunocompromised patients and in the southeastern and southwestern United States 1
• Common fungal pathogens:
  • Aspergillus species
  • Mucor
  • Pseudallescheria boydii (Scedosporium) 1

Special Clinical Scenarios

Nosocomial Sinusitis

• Gram-negative bacilli (Pseudomonas aeruginosa, Klebsiella pneumoniae, Enterobacter species)
• Staphylococcus aureus (including MRSA strains) 1, 3

Immunocompromised Patients

• Pseudomonas aeruginosa
• Fungi (invasive fungal sinusitis) 2

Important Clinical Considerations

• Diagnostic challenges: The precise microbial etiology of sinusitis can only be determined by direct aspiration of the sinus, as nasopharyngeal cultures correlate poorly with actual sinus pathogens 1

• Antimicrobial resistance: Many bacteria in sinusitis have developed resistance mechanisms:

  • Beta-lactamase production in H. influenzae, M. catarrhalis, S. aureus, and anaerobes
  • Penicillin-binding protein alterations in S. pneumoniae 4

• Biofilm formation: Chronic rhinosinusitis often involves biofilm formation, which contributes to persistence of infection and treatment resistance 3

• Treatment implications: Empiric antibiotic selection should target the most likely pathogens based on whether the infection is acute or chronic 1

Understanding the microbiology of sinusitis is essential for appropriate treatment selection, especially given the increasing prevalence of antimicrobial resistance among common respiratory pathogens.