Culture-Negative Infective Endocarditis

Blood culture–negative endocarditis (BCNE) is infective endocarditis in which routine blood cultures fail to grow the pathogen. A negative bottle does not mean a sterile valve. It may mean that antibiotics suppressed bacterial growth before sampling, or that the organism requires specialized methods—or cannot be recovered by routine culture at all. The resulting delay in targeted therapy contributes to worse outcomes than in culture-positive disease. Two mechanisms organize the differential: - Antibiotic-masked infection: Prior treatment most often suppresses methicillin-susceptible staphylococci, streptococci, and enterococci. Ask specifically about antibiotics taken for dental infections, skin infections, respiratory symptoms, or fever, including doses given at another facility. - Fastidious or non-culturable infection: Important causes include Coxiella burnetii, Bartonella species, Tropheryma whipplei, Brucella species, mycobacteria—including Mycobacterium chimaera—and fungi. An experienced clinician becomes suspicious when a patient has persistent or recurrent fever, a new murmur or valve dysfunction, heart failure, embolic findings, or an intracardiac prosthetic device despite sterile cultures. The history then changes the test order. Contact with sheep, goats, cattle, or parturient animals points toward Coxiella. Cats or fleas suggest Bartonella henselae; body lice...