Prosthetic Valve Endocarditis Resulting from Nosocomial Bacteremia

• Objective: To determine the incidence of endocarditis in bacteremic patients with prosthetic heart valves and the risk factors for and the effect of duration of antibiotic therapy on development of endocarditis in such patients. • Design: Multicenter, prospective observational study. • Setting: Six university teaching hospitals with highvolume cardiothoracic surgery. • Participants: One hundred seventy-one consecutive patients with prosthetic heart valves who developed bacteremia during hospitalization. • Measurements and Main Results: Patients were evaluated when they were identified as having bacteremia and 1,2,6, and 12 months after its occurrence. Of 171 patients, 74 (43%) developed endocarditis: Fifty-six (33%) had prosthetic valve endocarditis at the time bacteremia was discovered ("endocarditis at outset"), whereas 18(11%) developed endocarditis a mean of 45 days after bacteremia was discovered ("new endocarditis"). Mitral valve location and staphylococcal bacteremia (Staphylococcus aureus or S. epidermidis) were significantly associated with the development of "new" endocarditis. All 18 cases of new endocarditis were nosocomial, and in 6 of these cases (33%) bacteremia was acquired via intravascular devices. Twenty-one patients without evidence of endocarditis at the time of bacteremia received short-term antibiotic therapy ( 14 days) developed endocarditis (P > 0.2). • Conclusions: Bacteremic patients with prosthetic heart valves were at notable risk for developing endocarditis, even when they received antibiotic therapy before endocarditis developed and regardless of the duration of such therapy. Intravascular devices were a common portal of entry. M ore than 100 000 artificial heart valves are implanted annually in the United States, and the number is increasing (1). Because the number of invasive therapeutic and diagnostic procedures done during hospitalization is also increasing, the risk for bacteremia is correspondingly greater. A common dilemma for the clinician is determining the optimal therapeutic approach to a patient with a prosthetic valve who develops bacteremia. There has been controversy regarding the optimal duration of antibiotic therapy for bacteremic patients with prosthetic valves. An informal survey of infectious disease and cardiology specialists revealed that the recommended duration of therapy ranged widely, from 10 days to 8 weeks. To clarify this issue, we conducted a prospective, observational, multicenter study during a 3-year period in six university teaching hospitals with high-volume cardiac surgery. Our objectives were to determine 1) the incidence of endocarditis in bacteremic patients with an implanted heart valve, 2) the risk factors for development of subsequent prosthetic valve endocarditis, and 3) the optimal duration of antibiotic therapy in this select group of patients who experience bacteremia. We also report mortality rates.