Rosh Emergency Medicine Practice Test

What is the most common etiological agent of infective endocarditis in IV drug users?

1. Streptococcus viridans

2. Staphylococcus aureus

3. Enterococcus

4. HACEK organisms

The correct answer is: Staphylococcus aureus

Infective endocarditis is an infection of the inner lining of the heart and its valves, often associated with various risk factors including intravenous drug use. Among IV drug users, Staphylococcus aureus is the most common etiological agent responsible for this condition. This organism is particularly virulent and can readily enter the bloodstream through non-sterile injection practices commonly seen in this population. Staphylococcus aureus is adept at adhering to heart valves and is known for causing aggressive infections, leading to high morbidity and potential mortality if not treated promptly. In the context of IV drug use, the use of dirty needles introduces bacteria directly into the bloodstream, increasing the likelihood of infections with organisms such as Staphylococcus aureus. While other organisms like Streptococcus viridans and Enterococcus are also associated with infective endocarditis, they are more commonly involved in cases associated with underlying valvular heart disease or dental procedures rather than being specifically linked to intravenous drug use. HACEK organisms, although part of the endocarditis causative agents, are less prevalent as a cause in this particular group of patients. Their association is more notable in cases where there is a prior dental manipulative procedure or other specific risk factors unrelated to IV