Likelihood of Staphylococcus epidermidis Causing Endocarditis
Staphylococcus epidermidis is a predominant causative organism in prosthetic valve endocarditis (PVE), particularly in early PVE occurring within the first 2 months after valve surgery, but is a relatively uncommon cause of native valve endocarditis (approximately 5% of cases). 1
Incidence and Risk Factors
- S. epidermidis is the most common organism in early prosthetic valve endocarditis (within 2 months after surgery) 1
- In late prosthetic valve endocarditis (>1 year after surgery), the likelihood of S. epidermidis decreases significantly, with streptococci and S. aureus becoming more common 1, 2
- In native valve endocarditis, S. epidermidis accounts for only about 5% of cases, typically affecting patients with pre-existing valvular heart disease, particularly mitral valve prolapse 1, 3
- Healthcare-associated procedures involving intravascular devices significantly increase the risk of S. epidermidis endocarditis 1
Clinical Presentation and Course
- Native valve endocarditis caused by S. epidermidis typically follows an indolent course with a satisfactory response to medical or surgical therapy 1
- Prosthetic valve endocarditis caused by S. epidermidis often presents with:
- Fever
- New or changing heart murmurs
- Valve ring and myocardial abscesses (particularly with mechanical valves)
- Potential valve dehiscence and valvular incompetence 4
Antimicrobial Susceptibility
- S. epidermidis isolates from prosthetic valve endocarditis are frequently resistant to multiple antibiotics, including methicillin (87% of cases within 1 year of surgery) 2, 5
- Native valve S. epidermidis isolates are generally more susceptible to antibiotics than prosthetic valve isolates 3
- Vancomycin plus rifampin or an aminoglycoside is the recommended treatment for methicillin-resistant S. epidermidis prosthetic valve endocarditis 2
Mortality and Outcomes
- The mortality rate for prosthetic valve endocarditis caused by S. epidermidis is high (70-80%) when treated with antibiotics alone 3
- Surgical intervention significantly improves outcomes in complicated prosthetic valve endocarditis caused by S. epidermidis 2
- Native valve endocarditis caused by S. epidermidis has a considerably lower mortality rate compared to prosthetic valve infections 3
Special Considerations
- S. epidermidis should be distinguished from S. lugdunensis (another coagulase-negative staphylococcus), which causes a more virulent form of endocarditis with higher rates of perivalvular extension and metastatic infection 1
- Other coagulase-negative staphylococci like S. capitis can rarely cause prosthetic valve endocarditis with complications such as aortic root abscess 6
- Blood cultures may need to be incubated for longer periods to detect S. epidermidis in some cases of culture-negative endocarditis 1
Diagnostic Approach
- The modified Duke criteria should be used for diagnosis, with S. epidermidis blood cultures considered a major criterion only when multiple positive cultures are obtained (to distinguish from contamination) 1
- Transesophageal echocardiography is particularly important for detecting vegetations and complications in suspected prosthetic valve endocarditis 1