Infective endocarditis with negative blood cultures.

Culture-negative endocarditis is important as it has a relatively poor prognosis. The principal reason for negative cultures is prior antibiotic therapy although fastidious organisms such as Bartonella spp. and Coxiella burnetii are also important. PCR may offer significant advantages in diagnosis but tests require standardisation. Modification of current diagnostic criteria is required. Empirical cover of MRSA needs to be considered.