Background: Staphylococcus aureus is the leading cause of mortality in patients with infectious endocarditis. Despite intensive research, some debate still exists on risk factors for mortality and the role of valve replacement on outcome.
Methods: We conducted a retrospective review of cases of S. aureus endocarditis diagnosed with strict case definitions in a single institution and compared infection in patients with native and prosthetic valves.
Results: Eighty-four patients with definitive left-sided endocarditis were analyzed. The incidence of left-sided endocarditis caused by S. aureus ranged from 2 to 4 cases per 10,000 admissions per year. The mitral valve was more commonly involved than the aortic valve (58% vs 34%). Prosthetic valve endocarditis (PVE) was hospital acquired more frequently than native valve endocarditis (NVE) (21% vs 54%; odds ratio [OR], 0.24; 95% confidence interval [CI], 0.09-0.63). Bacteremia during effective antimicrobial therapy (25% vs 57%; OR, 0.25; 95% CI, 0.10-0.65), cardiac failure (43% vs 68%; OR, 0.36; 95% CI, 0.14-0.92), and central nervous system complications (28% vs 36%; OR, 0.72; 95% CI, 0.27-1.89) were more frequently observed in patients with PVE. The overall mortality was 33%, and it was lower in cases of NVE (28% vs 43%; OR, 0.52; 95% CI, 0.21-1.37). Patients without complications survived the infection, but a trend toward a higher mortality in patients who developed 1 (19%), 2 (40%), or 3 (83%) complications was observed (Spearman ρ = 0.568; P < 0.001). Valve replacement was more frequently performed in patients with PVE (37% vs 71%; OR, 0.24; 95% CI, 0.09-0.64). Among patients with NVE, no single complication was significantly associated with mortality, and we did not find survival advantage of surgical treatment. In cases of PVE, surgical treatment determined a survival benefit (OR, 0.02; 95% CI, 0.00-0.33).
Conclusions: Clinical and prognostic differences do exist between NVE and PVE due to S. aureus. The sum of cardiac, renal, and central nervous system complications was the main determinant of mortality. Although cardiac surgery did not determine a survival benefit in patients with NVE, valve replacement seemed to improve the survival rate in patients with PVE.