Bacteriological outcome of combination versus single-agent treatment for staphylococcal endocarditis

Objective: To analyse the bacteriological outcome of combination versus single-agent antimicrobial treatment in staphylococcal endocarditis. Patients and methods: Retrospective review of 152 episodes: 91 cases of native valve endocarditis (NVE), 74 due to Staphylococcus aureus and 17 due to coagulase-negative staphylococci (CoNS); and 61 cases of prosthetic valve endocarditis (PVE), 29 due to S. aureus and 32 due to CoNS. Results: Valves from patients with S. aureus NVE treated with any kind of combination antibiotic treatment were no more likely to be culture-negative than those treated with a single agent [19 (45%) of 42 versus 13 (41%) of 32; P=0.69]. This finding remained unchanged when cases of CoNS NVE were added to the S. aureus group. In PVE, after adjusting for duration of treatment, valves from patients receiving any kind of combination treatment were 5.9 times (95% confidence interval 1.3-27.5) more likely to be culture-negative than those receiving monotherapy (P=0.024). Patients treated for >14 days were more likely to be culture-negative than those treated for less than or equal to14 days [49 (83%) of 59 versus 29 (31%) of 93; P<0.001]. Conclusions: In staphylococcal NVE, combination treatment is not superior to monotherapy in sterilizing infected valves, but in PVE combination treatment confers an advantage.