Brain Abscess

PATHOGENS

• In 80-90% of abscesses, multiple organisms are found.
• Streptococci most common single organisms identified (30-50%), but anaerobic or other aerobic organisms can predominate.
• Gram negatives are more common in infants.
• Fungal causes include candida spp., aspergillus, zygomycetes.
• Most series of pyogenic abscess ~25% unknown source (cryptogenic).
• Source or host specifics:
  • Paranasal sinusitis: microaerophilic (S. intermedius group) and anaerobic strep, Haemophilus species, Bacteroides spp, Fusobacterium spp, Prevotella spp.
  • Otogenic infection: aerobic and anaerobic streptococci, Enterobacteriaceae, Pseudomonas aeruginosa , Prevotella spp, B. fragilis.
  • Odontogenic infection: S. viridans and anaerobic streptococci, Bacteroides spp, Fusobacterium spp, Prevotella spp, Actinomyces spp.
  • Endocarditis: Staphylococcus aureus, S. viridans, Enterococcus. Lung abscess: microaerophilic and anaerobic streptococci, Actinomyces species, Fusobacterium species, Nocardia species, Prevotella.
  • Penetrating trauma: Staphylococcus aureus, aerobic streptococci, Clostridium species, Enterobacteriaceae.
  • Postoperative: Staphylococcus epidermidis, S. aureus, Enterobacteriaceae, Pseudomonas aeruginosa.
  • Right to left shunt (congenital heart disease): microaerophilic and aerobic streptococci.
  • Compromised host (AIDS, cancer chemotherapy, chronic steroids, lymphoma): toxoplasmosis, nocardia, EBV lymphoma, TB, fungal.
  • Immigrant: cysticercosis, echinococcus, TB (tuberculoma).