Culture-negative endocarditis - causes, diagnosis and treatment

Infective endocarditis (IE) is associated with high morbidity and mortality . This infection is difficult to diagnose and, in some cases, to treat succ essfully particularly when the causative agent is non-culturable. Blood cul ture is still the most important laboratory test performed during the diagn ostic work-up of IE. The bacteraemia associated with the disease is usually continuous and low grade. In two-thirds of all IE cases the blood cultures taken will be positive and will usually reveal a variety of aetiological a gents depending on the patient population. Streptococcus spp. are the main causative agents in patients who have an intact immune system and possess n ative heart valves. Staphylococci are the predominant microorganisms in pat ients with prosthetic heart valves and in intravenous drug abusers. Other m iscellaneous bacteria and fungi may also cause IE. However between 5 and 24 % of suspected IE cases yield negative blood culture results; there are se veral possible explanations for this, including prior antibiotic therapy, f astidious and cell-dependent organisms or fungi. Ultimately the identificat ion of the causative agent is the cornerstone of successful treatment of IE through appropriate chemotherapy. Conventional methodologies cannot detect the causative agent in culture-negative IE cases and hence difficulties ar ise in the clinical management of such patients. The aim of this review is to examine: (i) the reasons contributing to culture-negative IE; (ii) diagn ostic criteria for the classification of IE; (iii) diagnostic methodology o f IE, particularly trends in the application of molecular-based techniques; (iv) aetiological agents responsible for culture-negative IE; and (v) trea tment of IE. (C) 2000 Lippincott Williams & Wilkins.