Culture-negative endocarditis—causes, diagnosis and treatment

Abstract

Infective endocarditis (IE) is associated with high morbidity and mortality. This infection is difficult to diagnose and, in some cases, to treat successfully particularly when the causative agent is non-culturable. Blood culture is still the most important laboratory test performed during the diagnostic 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 agents depending on the patient population.Streptococcusspp. are the main causative agents in patients who have an intact immune system and possess native heart valves. Staphylococci are the predominant microorganisms in patients with prosthetic heart valves and in intravenous drug abusers. Other miscellaneous bacteria and fungi may also cause IE. However between 5 and 24% of suspected IE cases yield negative blood culture results; there are several possible explanations for this, including prior antibiotic therapy, fastidious and cell-dependent organisms or fungi. Ultimately the identification 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 arise in the clinical management of such patients. The aim of this review is to examine: (i) the reasons contributing to culture-negative IE; (ii) diagnostic criteria for the classification of IE; (iii) diagnostic methodology of IE, particularly trends in the application of molecular-based techniques; (iv) aetiological agents responsible for culture-negative IE; and (v) treatment of IE. © 2000 Lippincott Williams & Wilkins