Microbiology of Infective Endocarditis

• 95% of cases of infective endocarditis:

  • Affect the left side of the heart
  • Mitral and aortic valves affected equally
• Acute infective endocarditis:

  • Most often caused by Staphylococcus aureus
  • Equally prevalent on normal and abnormal valves
  • Rare
• Right-sided endocarditis in intravenous drug abuse:

  • 5% of cases
  • Tricuspid valve
  • Usually presents acutely in IV drug abusers or the immunocompromised
• Risk factors for infective endocarditis:

  • Congenital lesions
  • Vascular abnormalities
  • IV drug abuse
  • Abortion
  • Prosthetic valve
  • Cardiac/urinary catheterisation
  • Any invasive diagnostic or surgical procedure, eg: dental (see latest NICE advice), or urological
• Risk factors for infective endocarditis - congenital lesions:

  • Ventricular septal defect
  • Tetralogy of Fallot (a birth defect that affects normal blood flow through the heart)
  • Coartication of aorta (narrowing of the aorta close to ductus arteriosus)
  • Patent ductus arteriosus
• Risk factors for infective endocarditis - vascular abnormalities:

  • Rheumatic involvement of any valve - but now less important in developed countries
  • Bicuspid or calcific aortic valve
  • Subaortic stenosis
  • Mitral valve prolapse
• Bacterial endocarditis:

  • Most common
  • Damaged valves/elderly
  • Common causes
  • Oral streptococci
  • Staphylococci
  • Faecal streptococci
• Acute form of infective endocarditis related to more virulent microorganisms, like staphylococcus aureus - MRSA