• Duke criteria
• culture negative endocarditis
• endocarditis

The diagnosis of infective endocarditis with its multiple clinical and morphological manifestations remains a challenging task. The von Reyn criteria, published in 1981, focused mainly on clinical and pathological findings in combination with positive blood culture to diagnose infective endocarditis.¹ They were helpful to standardise diagnostic criteria, but their positive and negative predictive values remained unacceptably low, especially in the absence of positive blood culture results. With the introduction of transoesophageal echocardiography for the diagnosis of infective endocarditis,² and the implementation of this method into the diagnostic criteria by Durack and colleagues,³ sensitivity and specificity of the diagnosis was significantly increased.⁴ Yet, in culture negative cases, sensitivity of these Duke criteria remains limited.^5,6

In most cases, there are two reasons for negative blood cultures: (1) patients received antibiotics before blood cultures are taken due to systemic infection or suspected diagnosis of a bacterial infection; and (2) the causative microorganisms have no, or limited proliferation in conventional blood cultures, or the diagnosis of the causative microorganisms requires special media or cell culture conditions. Negative blood cultures occur in 2.5–31% of all cases of infective endocarditis, which often delays diagnosis and onset of treatment with profound impact on the clinical outcome.⁷ The difficulties arising from culture negativity in cases of suspected endocarditis may be illustrated by a recent example from our institution.

In November 2001, a 68 year old man was submitted to our department after syncope of unclear origin. The patient had undergone aortic valve replacement (Saint Jude 29.0 mm) …