Karius Medical Case Reports: Blood Culture-Negative Endocarditis | Karius
  • Filters
  • only
  • only
  • only
  • only
  • only
  • only
  • only
  • only
  • only
  • only

Select All / Deselect All


Karius Medical Case Reports: Blood Culture-Negative Endocarditis

Blood culture-negative endocarditis is an infection of the heart valves where blood cultures to determine the causative pathogen are negative. Up to 31% of all cases of bacterial endocarditis may be culture-negative, creating challenges for diagnosis and management1.

Patients with endocarditis typically present with fevers, night sweats, and weight loss -- often for weeks or months. Risk factors for endocarditis include congenital heart disease, pre-existing valve disease or prosthetic valves, and injection drug use.

Blood cultures in bacterial endocarditis typically reveal a causative pathogen within 48 hours. However, patients with culture-negative endocarditis have often been pre-treated with antibiotics or are infected with fastidious, slow-growing bacteria that do not grow well in blood culture2.


Some of the bacterial species that are associated with culture-negative endocarditis include3:

  • Bartonella henselae (“cat-scratch disease”)

  • Brucella melitensis (from consuming unpasteurized milk)

  • Coxiella burnetii (from inhalation of aerosols from cows, sheep, goats)

  • Legionella pneumophila (from aerosolized water supply)

  • HACEK organisms including species of Haemophilus, Aggregatibacter, Cardiobacterium, Eikenella, and Kingella (normal oral flora that cause approximately 3% of endocarditis)


In culture-negative endocarditis, a definitive diagnosis generally requires serologic testing, PCR assays, or culture of the infected heart valve tissue - however in up to 51% of cases, no causative pathogen is identified4.

There is a clear need for rapid, sensitive, noninvasive methods for accurate identification of organisms causing endocarditis to enable early, precisely targeted therapy.

We have demonstrated the use of the Karius™ Test in identifying pathogens associated with culture-negative endocarditis. The following are selected medical case reports that illustrate the efficacy and utility of the Karius Test for this purpose.

A complete list of pathogens that the Karius Test can detect is located here.



Clinical Scenario: A middle-aged male who spends a great deal of time outdoors presented with several months of fevers, night sweats, weight loss, and headaches. He was found to have a cerebral aneurysm, with high suspicion for endocarditis despite inconclusive echocardiography. Blood cultures and multiple serologies were negative. A Karius Test was sent.

Karius Test Result: Bartonella henselae

Based on this result, the treatment was switched to target Bartonella as a cause of BCNE. Repeat serologies were also sent and eventually turned positive for Bartonella antibodies. Karius was able to identify the causative agent when other conventional testing was negative, and more rapidly than serologic testing.



Clinical Scenario: A pediatric patient with a history of mitral valve replacement was admitted with fever and tachycardia; a large vegetation was visualized on the prosthetic mitral valve. Initial blood cultures were negative and the patient was started on empiric treatment for prosthetic valve endocarditis. The patient began developing toxicities (thrombocytopenia) related to antibiotic treatment with linezolid + doxycycline. A Karius Test was sent.

Karius Test Result: Kingella kingae, a HACEK organism

After receiving the result, the physician was able to switch the patient’s treatment to a less toxic regimen and his platelet count improved. He ultimately underwent prosthetic valve replacement, with bacterial 16S ribosomal sequencing of the explanted valve confirming Kingella kingae infection. Karius was able to non-invasively identify the causative organism in prosthetic valve endocarditis prior to definitive surgical diagnosis.


In these cases, the Karius Test was able to accurately identify specific pathogens within a clinically relevant timeframe, enabling the clinicians to provide more timely and precise treatment to their patients. We will discuss additional case reports in future posts.



  1. Fournier P-E et al. Comprehensive Diagnostic Strategy for Blood Culture-Negative Endocarditis: A Prospective Study of 819 New Cases. Clinical Infectious Diseases (2010) 51(2):131–140.

  2. Van Scoy RE. Culture-negative endocarditis. Mayo Clinic Proceedings (1982) 57(3):149-154.

  3. Houpikian P and Raoult D. Blood Culture-Negative Endocarditis in a Reference Center: Etiologic Diagnosis of 348 Cases. Medicine (2005) 84(3):162-173.

  4. Lamas CC and Eykyn SJ. Blood culture negative endocarditis: analysis of 63 cases presenting over 25 years. Heart (2003) 89:258-262.


DISCLAIMER: Case descriptions have been modified to protect patient privacy and, while every attempt has been made to provide accurate information, errors may occur. This information is provided for educational purposes only, and is not intended to be used as medical advice.