Culture-negative endocarditis: Etiology, diagnosis, management and treatment

Background: Culture-negative endocarditis is a diagnostic challenge with va riable clinical presentation and protean manifestations. Etiology and Diagnosis: The two main causes why endocarditis may be culture -negative are 1. antibiotic treatment prior to obtaining blood cultures, an d 2. the presence of fastidious microorganisms with limited or no capacity to grow in routine blood cultures (Table 1). If initial blood cultures rema in negative for 48-72 hours, these cultures should be incubated for at leas t an additional 2-4 weeks. Moreover, subcultures should be plated onto choc olate agar and incubated in an atmosphere of increased CO2 environment to f acilitate recovery of fastidious bacteria. Additional techniques for identi fication of a causative organism include serologic tests and DNA/RNA-based molecular techniques. If the patient is clinically stable, the clinician ca n wait until culture results from initial samples are known before deciding upon either administering an empiric antibiotic therapy or obtaining furth er blood cultures. Certain predisposing patient characteristics or epidemio logic exposures may be associated with particular causative microorganisms in culture-negative endocarditis. In the absence of positive blood cultures echocardiography is a crucial tool in the diagnosis and management of cult ure-negative endocarditis which provides the basis for the visualization of endocarditis-associated cardiac lesions. In this context, transesophageal echocardiography is associated with a significantly higher sensitivity in t he detection of vegetations and perivalvular complications and is, therefor e, considered the diagnostic imaging method of choice in the diagnosis of c ulture-negative endocarditis. The Duke criteria have been shown to have a h igh accuracy in the diagnosis of culture-negative endocarditis. In this con text global clinical judgment demonstrated a comparable sensitivity but a l ower specificity. Main differential diagnoses include diseases which can mi mic the clinical endocarditis syndrome as well as the echocardiographic pat tern of culture-negative endocarditis, especially 1. nonbacterial thromboti c endocarditis and 2. valvular sclerosis in the presence of systemic infect ion (Table 2). Treatment: The selection of a particular antibiotic regimen in a suspected case of culture-negative endocarditis depends on demographics (e.g., age or geographic area), epidemiologic history (e.g., animal exposures, drug-use history, alcohol abuse, homelessness) and clinical characteristics which ma y be suggestive of an etiologic organism.