Mitral valve prolapse and bacterial endocarditis: when is antibiotic prophylaxis necessary?

We investigated the association between mitral valve prolapse (MVP) and bacterial endocarditis (BE) in a case-control study of 56 patients with BE and 168 age- and sex-matched controls who had had echocardiography. Cases and controls were selected from patients without other known cardiovascular risk factors for BE. Twenty percent of the BE cases (11 of 56) and 4% of the controls (7 of 168) had MVP; the odds ratio of 5.3 (95% confidence interval 2.0 to 14.4) indicated a significantly greater risk of BE in patients with MVP. This increased those who had preexisting systolic murmurs (9 of 11). Exposure to repeated vascular instrumentation also increased the risk of BE (odds ratio 6.2, 95% confidence interval 2.3 to 16.4); this was independent of the risk associated with MVP. Based upon these data and the incidence of BE in New South Wales, Australia, in 1980, we estimate that 14 of every 100,000 adult patients with MVP would develop BE over a 1-year period, compared with three people in every 100,000 without other known risk factors for BE in the general population. Thus, although the risk of BE is five times greater in patients with MVP, the absolute risk remains small. This indicates that antibiotic prophylaxis is unnecessary for the majority of patients with MVP. We suggest that for patients with MVP not otherwise known to be at high risk of BE, routine antibiotic prophylaxis should be advised only for those who have systolic murmurs.