Infective endocarditis

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)
• rheumatic valve disease (30%)
• prosthetic valves
• congenital heart defects
• intravenous drug users (IVDUs, e.g. typically causing tricuspid lesion)

Causes

• historically Streptococcus viridans was the most common cause of infective endocarditis. This is no longer the case, except in developing countries. Staphylococcus aureus is now the most common cause of infective endocarditis. Staphylococcus aureus is also particularly common in acute presentation and IVDUs
• 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 viridans still accounts for around 20% of cases. 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
• Streptococcus bovis is associated with colorectal cancer
• non-infective: systemic lupus erythematosus (Libman-Sacks), malignancy: marantic endocarditis

Culture negative causes

• prior antibiotic therapy
• Coxiella burnetii
• Bartonella
• Brucella
• HACEK: Haemophilus, Actinobacillus, Cardiobacterium, Eikenella, Kingella)

*Lancet 2016; 387: 882-93 Infective Endocarditis