Blood Infections with Negative Blood Cultures

Causes of Culture-Negative Blood Infections

The American Heart Association notes that administration of antimicrobial agents before blood cultures are obtained reduces the recovery rate of bacteria by 35-40% 1, 3
The antimicrobial susceptibility of the organism, dose, duration, and nature of previous therapy determine how long blood cultures will remain negative, according to the American College of Cardiology 2, 3
Patients with only a few days of prior antibiotic therapy may have positive cultures after several days without antibiotics, while those on longer courses may have negative cultures for weeks, as stated by the American Heart Association 2

The American College of Cardiology recommends collecting at least three sets of blood cultures from different sites, with each set including one aerobic and one anaerobic bottle with adequate blood volume (5-10 ml per bottle for adults) 3
For patients with suspected infective endocarditis who have received antibiotics, the American Heart Association suggests waiting at least 3 days after antibiotic discontinuation before obtaining cultures 3
Echocardiography is crucial for diagnosis of infective endocarditis, with transesophageal echocardiography detecting vegetations in >95% of patients, according to the American College of Cardiology 5

In culture-negative infective endocarditis, empiric antimicrobial therapy should be guided by epidemiological factors and clinical course, as recommended by the American Heart Association 6
For native valve culture-negative endocarditis, 4-6 weeks of treatment is recommended by the American College of Cardiology 3
Consultation with an infectious diseases specialist is strongly recommended for management of culture-negative endocarditis, according to the American College of Cardiology 2, 3