Prognostic role of persistent positive blood cultures after initiation of antibiotic therapy in left-sided infective endocarditis

Persistent infection is not a scientific evidence-based definition. The guidelines of infective endocarditis (IE) establish a cut-off point of 7–10 days, which is arbitrary and probably too long. Our hypothesis is that persistent positive blood cultures after 48–72 h from the initiation of antibiotic therapy are associated with a worse prognosis in patients with left-sided IE.

We repeated blood cultures after 48–72 h of the initiation of the antibiotic treatment in 407 patients with left-sided IE of a total of 692 episodes consecutively diagnosed from 1996 to 2011. We have compared the profile of patients whose blood cultures became negative and those with persistent positive blood cultures. We performed a multivariate logistic regression model to determine the prognostic implication of persistent positive blood cultures.

Of 256 patients with positive blood cultures at admission, 89 (35%) had persistent positive cultures after 48–72 h from the initiation of the antibiotic treatment. Persistent positive blood cultures (OR: 2.1; 95% CI: 1.2–3.6), age (OR: 1.026; 95% CI: 1.007–1.046), Staphylococcus aureus infection (OR: 3.3; 95% CI: 1.6–6.6), heart failure (OR: 2.8; 95% CI: 1.6–4.7), and renal failure (OR: 2.9; 95% CI: 1.8–4.9) were found to be independently associated with higher in-hospital mortality.

The presence of persistent positive blood cultures is an independent risk factor for in-hospital mortality which doubles the risk of death of patients with left-sided IE. It should be taken into account in the risk stratification of these patients.