Differences between endocarditis with true negative blood cultures and those with previous antibiotic treatment

High morbidity and mortality are attributed to patients with culture-negative endocarditis. The main reason for negative blood culture in infectious endocarditis (IE) is administration of antibiotics before sample withdrawal. The study aim was to determine any difference in prognosis between patients with 'aborted' culture-negative endocarditis (A-CNE) and those with true culture-negative endocarditis (T-CNE).

A total of 107 patients with a diagnosis of IE was studied retrospectively. Diagnosis was confirmed pathologically during surgery, at post-mortem examination, or by fulfillment of Duke's criteria. Twenty patients (18.7%) had negative-culture endocarditis and comprised the study population. Of these patients, 14 (70%) had received previous antibiotic therapy (A-CNE), and six (30%) were considered T-CNE cases. In-hospital outcome and clinical characteristics were compared between both patient groups. The main end-point was death or need for surgical repair of the heart valves during hospitalization.

There were no significant inter-group differences with respect to mean age, gender distribution, and other clinical characteristics. The composite endpoint of death or surgical repair occurred more frequently in T-CNE patients (100% versus 64%, p = 0.0394). Anatomic complications also occurred more frequently in T-CNE patients, but the difference was statistically not significant.

Among patients with IE and a negative blood culture, those without previous antibiotic therapy (T-CNE) have the worse prognosis.