Clinical Significance of Tolerant Strains of Staphylococcus aureus in Patients with Endocarditis

Abstract

Cases (50) of endocarditis and 54 cases of bacteremia due to S. aureus were studied to ascertain the clinical significance of the newly described phenomenon of tolerance. In 32 of the patients with endocarditis and 35 of those with bacteremia strains were classified as tolerant (minimum bactericidal concentration/minimum inhibitory concentration .gtoreq. 16). Patients with endocarditis due to a tolerant strain responded less favorably than did patients with a sensitive strain. A larger number of patients with a tolerant strain had prolonged fever (58 vs. 19%), a higher mean number of complications (1.6 vs. 0.73), a greater number of intensive-care unit admissions (66 vs. 33%) and a higher mortality (25 vs. 11%). There was no difference in response to therapy in bacteremic patients without endocarditis having sensitive and tolerant strains. Infection with a tolerant organism adversely influences the outcome of staphylococcal endocarditis.