Is Staphylococcus aureus the most common etiology of endocarditis in Intravenous (IV) drug users?

From the Guidelines

Intravenous (IV) drug use is a significant risk factor for Staphylococcus aureus endocarditis, with S. aureus being the leading cause of infective endocarditis in IV drug users, accounting for approximately 60-70% of cases in this population. The pathophysiology involves direct injection of skin flora (particularly S. aureus, which commonly colonizes the skin) into the bloodstream during injection drug use 1. The repeated trauma to the skin and use of non-sterile equipment introduces bacteria directly into the circulation. Once in the bloodstream, S. aureus has multiple virulence factors that allow it to adhere to heart valves, particularly the tricuspid valve in IV drug users. This right-sided endocarditis is characteristic of IV drug use-associated infections, though left-sided valves can also be affected.

Some key points to consider in the management of S. aureus endocarditis in IV drug users include:

• The use of antimicrobial therapy guided by identification of the causative organism 1
• The importance of covering S. aureus with the antibiotic regimen, using either penicillinase-resistant penicillins or vancomycin, depending on the local prevalence of MRSA 1
• The need for early recognition and appropriate antibiotic therapy to prevent complications and improve outcomes 1
• The consideration of substance use disorder treatment, harm reduction approaches, and proper skin antisepsis before medical procedures as prevention strategies 1

It is essential to note that the management of S. aureus endocarditis in IV drug users requires a comprehensive approach, including medical and surgical interventions, as well as addressing the underlying substance use disorder. The most recent and highest quality study 1 recommends a minimum of 4 to 6 weeks of intravenous antibiotic therapy, with the option of adding gentamicin for the first 3 to 5 days, and emphasizes the importance of individualized care and consultation with infectious diseases specialists and cardiothoracic surgeons.

From the Research

Etiology of Endocarditis

• The most common etiology of endocarditis is Staphylococcus aureus, which can originate from various sources, including nosocomial sources, intravenous drug use, and prosthetic valves 2.
• Staphylococcus aureus is the leading cause of infectious endocarditis, and its mortality has remained high despite better diagnostic and therapeutic procedures over time 3.

Role of IV Drug Use

• Intravenous drug use is a significant risk factor for acquiring infective endocarditis, particularly right-sided endocarditis 2, 3.
• The incidence of endocarditis caused by Staphylococcus aureus is higher among intravenous drug users, with a reported incidence of 2.5/1000 person-years in one study 4.
• Mortality rates for endocarditis caused by Staphylococcus aureus are lower in intravenous drug users (3.7%) compared to non-drug users (15%) 3.

Epidemiology and Outcome

• The epidemiology of Staphylococcus aureus bacteremia and endocarditis has been changing over the past decades, with an increasing incidence in many regions 4.
• The overall mortality of patients with Staphylococcus aureus endocarditis is high, ranging from 20-30% in-hospital mortality, with symptomatic cerebral embolizations being common (12-35%) 4.
• Valve replacement is often needed in patients with prosthetic valve endocarditis, but active intravenous drug use may be a reason to refrain from surgery 3.