Infective endocarditis in intravenous drug abusers (IDA) refers to a type of infective endocarditis (IE) that primarily affects the right heart system in individuals who inject drugs intravenously, with the tricuspid valve being the most commonly involved site. The incidence in IDA is 30 times higher than that in the general population, particularly in patients with HIV antibody positivity or immunodeficiency.
Staphylococcus aureus is the predominant pathogen, accounting for 60%-90% of cases, with methicillin-resistant Staphylococcus aureus (MRSA) being the most common strain. Other causative pathogens include streptococci, Gram-negative bacilli, and fungi. The pathogenic organisms often originate from the skin and less commonly from the drugs themselves.
The primary clinical manifestations include persistent fever, bacteremia, and multiple infectious pulmonary emboli. Isolated right heart failure is rare and may result from pulmonary hypertension or severe right-sided valvular regurgitation or obstruction. Cardiac murmurs are generally absent when the tricuspid valve is involved. The clinical features distinguishing this condition from native valve endocarditis (NVE) include the following:
- This predominantly affects normal valves, most commonly the tricuspid valve, followed by the pulmonary valve, with left-sided valves being less frequently involved.
- Acute onset is common and is often associated with pulmonary septic emboli, which may present as multiple patchy infiltrates on chest X-rays caused by vegetations on the tricuspid or pulmonary valves.
- Subacute onset is more frequently observed in patients with a history of IE.
The choice of antibiotic therapy depends on the causative pathogen, the type of drug and solvent used, and the site of infection. For most patients with uncomplicated tricuspid valve IE, a two-week course of nafcillin (or oxacillin) monotherapy is appropriate if all of the following conditions are met: methicillin-sensitive Staphylococcus aureus (MSSA) infection, absence of metastatic foci or abscesses, absence of intracardiac or extracardiac complications, no involvement of prosthetic valves or left-sided valves, vegetations <20 mm in size, and no severe immunosuppression (CD4 > 200/μl). A standard 4-6 week treatment regimen is required if any of the following conditions are present:
- Slow clinical response to antibiotics (lasting >96 hours).
- Right-sided IE complicated by right heart failure, acute respiratory failure, vegetations >20 mm, extracardiac septic emboli, or other extracardiac complications.
- Severe immunosuppression in intravenous drug abusers (CD4 < 200/μl).
- Involvement of left-sided valves.
Surgical intervention is generally avoided in patients but may be considered in the following situations:
- Severe tricuspid regurgitation causing right heart failure that does not respond well to diuretics.
- Infections caused by difficult-to-eradicate pathogens (e.g., fungi) or persistent bacteremia despite at least seven days of adequate antibiotic therapy.
- Tricuspid valve vegetations >20 mm causing recurrent pulmonary emboli.
The mortality rate in young patients with right-sided Staphylococcus aureus infections is less than 5%. Poor prognostic factors include involvement of left-sided valves (especially the aortic valve), vegetations >20 mm, infections caused by Gram-negative bacilli or fungi, and HIV infection with CD4 counts <200/μl.