Clinical significance of tolerant strains of Staphylococcus aureus in patients with endocarditis.

We have studied 50 cases of endocarditis and 54 cases of bacteremia due to Staphylococcus aureus 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 greater than or equal to 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% versus 19%), a higher mean number of complications (1.6 versus 0.73), a greater number of intensive-care unit admissions (66% versus 33%), and a higher mortality (25% versus 11%). In contrast there was no difference in response to therapy in bacteremic patients without endocarditis having sensitive and tolerant strains. We conclude that infection with a tolerant organism adversely influences the outcome of staphylococcal endocarditis.