Is It Useful to Repeat Blood Cultures in Endocarditis Patients? A Critical Appraisal

Background: for patients with endocarditis, guidelines recommend repeating blood cultures until they become negative, but with very limited evidence. Methods: a literature review was done on the incidence and duration of persistent bacteremia and persistent fever in endocarditis patients, compared to their associations with persistent infection at day 7. Results: persistent bacteremia and persistent fever are common in the first few days after starting antibiotic therapy, a normal duration for either at or around < 3-7 days. Persistent bacteremia is more prevalent and longer lasting in Staphylococcus (especially MRSA) and Enterococcus species than in Streptococcus species. In one study the risk for persistent infection at day 7 was 50% in those with positive blood cultures at 48-72 hours while it was 32% in those with negativization of blood cultures. Both persistent bacteremia at 48-72 hours and persistent infection at day 7 are predictive of in-hospital mortality. Conclusion: persistent bacteremia after treatment for endocarditis is common and often accompanied by persistent fever. Persistent infection at 7 days (as indication for urgent surgery) cannot be reliably predicted by positive or negative blood cultures at 48-72 hours. The recommendation of performing survey blood cultures in all patients therefore needs to be reconsidered.