More than 70% of infective endocarditis (IE) cases occur in native valves as a result of platelet aggregation due to valves that are damaged or have altered flow dynamics.
Mitral valve prolapse is the most common risk factor and raises risk for IE 8-fold.
Impurities in injectable drugs cause valvular damage, typically damaging the tricuspid valve through microtrauma. This area subsequently becomes a nidus for infection.
Staphylococcus aureus is the leading cause of IE. Other major causes are Streptococcus viridans, enterococci, and coagulase-negative staphylococci. Blood-culture-negative IE accounts for one-third of cases.
IE should be considered in any patient with > 1 week of fever that is consistent or intermittent.