Infective endocarditis:

Aetiology

The strongest risk factor for developing infective endocarditis is a previous episode of endocarditis. The following types of patients are affected:

• previously normal valves (50%, typically acute presentation)
  • the mitral valve is most commonly affected
• rheumatic valve disease (30%)
• prosthetic valves
• congenital heart defects
• intravenous drug users (IVDUs)
  • e.g. typically causing tricuspid lesion)
• others: recent piercings

Causes

• Staphylococcus aureus
  • now the most common cause of infective endocarditis
  • particularly common in acute presentation and IVDUs
• Streptococcus viridans
  • historically Streptococcus viridans was the most common cause of infective endocarditis. This is no longer the case, except in developing countries
  • technically Streptococcus viridans is a pseudotaxonomic term, referring to viridans streptococci, rather than a particular organism. The two most notable viridans streptococci are Streptococcus mitis and Streptococcus sanguinis
  • they are both commonly found in the mouth and in particular dental plaque so endocarditis caused by these organisms is linked with poor dental hygiene or following a dental procedure
• coagulase-negative Staphylococci such as Staphylococcus epidermidis
  • commonly colonize indwelling lines and are the most cause of endocarditis in patients following prosthetic valve surgery, usually the result of perioperative contamination.
  • after 2 months the spectrum of organisms which cause endocarditis return to normal (i.e. Staphylococcus aureus is the most common cause)
• Streptococcus bovis
  • associated with colorectal cancer
  • the subtype Streptococcus gallolyticus is most linked with colorectal cancer
• non-infective
  • systemic lupus erythematosus (Libman-Sacks)
  • malignancy: marantic endocarditis

Culture negative causes

• prior antibiotic therapy
• Coxiella burnetii
• Bartonella