Culture-negative endocarditis
Baddour, 2015Habib, 2015Subedi, 2017
Endocarditis with negative culture results is commonly associated with prior antibiotic therapy, but may be caused by unusual pathogens, such as:
- fastidious gram-positive cocci
- Bartonella species
- Coxiella burnetii (Q fever)
- Tropheryma whipplei (Whipple disease)
- Brucella species
- fungi
- Legionella species
- Mycobacterium chimaera.
Perform Q fever, Legionella and Bartonella (cat-scratch) serology and consider performing Brucella serology in recent immigrants and travellers from endemic areas (eg Middle East, southern Europe) and in hunters of feral pigs. M. chimaera is a rare cause of culture-negative endocarditis, which may occur in the setting of recent cardiac surgery1Stewardson, 2017. Overall, medically-treated cases of culture-negative endocarditis tend to have a higher mortality than for culture-positive casesKong, 2022. Seek expert advice for all cases of culture-negative endocarditis – see Approach to managing infective endocarditis.
Evaluate the patient for alternative, noninfective diagnoses. If microbiological tests remain negative, consider a neoplastic or autoimmune causeBaddour, 2015.
If the patient requires cardiac surgery, histopathology and 16S ribosomal RNA sequencing of valve tissue may provide a diagnosis.
If a pathogen is not identified despite investigation and an infection remains the likely diagnosis, treat empirically with 4 to 6 weeks of antibiotics. The choice of antibiotics depends on the clinical setting, including whether antibiotic therapy was given before samples for blood culture were taken, and whether the endocarditis involves native or prosthetic valves.
Management of Q fever endocarditis is complex and should include consultation with an endocarditis team. Treatment of Q fever endocarditis usually requires therapy with a doxycycline-based regimen, for a prolonged duration depending on the clinical circumstances. For further information on Q fever, see Q fever.
For the management of Bartonella endocarditis, see Bartonella infections.