Culture-negative endocarditis

Differential Diagnosis

Common Fastidious Organisms

Organism	Clinical clues	Diagnostic tests
Brucella	unpasteurized dairy	blood cultures, serology, culture, immunohistology, PCR
Coxiella burnetii	animal exposure (especially pregnant sheep)	serology (IgG phase I >1:800), tissue culture, immunohistology, PCR
Bartonella	cat exposure, louse exposure, crowding, homelessness	blood cultures, serology, culture, immunohistology, PCR
Tropheryma whipplei		histology and PCR
Mycoplasma		serology, culture, immunohistology, PCR
Legionella		blood cultures, serology, culture, immunohistology, PCR
Fungi	IV drug use, immunocompromise	blood cultures, serology, PCR

Organisms by Risk Factor

• Homelessness with body lice: Bartonella quintana
• Occupational exposures
  • Butchers, fishermen, homemakers, veterinarians, farmers: Erysipelothrix rhusiopathiae
  • Farmers, veterinarians: Coxiella burnetii, Brucella
• Intravenous drug use:
  • Right-sided with advanced HIV: Salmonella, Neisseria subflava
  • Pharyngitis: Corynebacterium diphtheriae
  • Other: Neisseria sicca, Clostridium, Candida
• Open heart surgery: Legionella, non-tuberculous mycobacteria including Mycobacterium avium complex, Nocardia
• Gastroenteritis: Salmonella
• Sinusitis: Haemophilus influenzae
• Pneumonitis: Chlamydia psittaci
• Diarrhea: Tropheryma whipplei
• Urinary tract infection: Klebsiella
• Dental procedures: Kingella kingae, Cardiobacterium hominis, Actinobacillus actinomicetemcomitans, Haemophilus parainfluenzae, Lactobacillus speies
  • Cirrhosis and alcoholism: Campylobacter fetus
  • Immunocompromised patient: Gemella
  • Intravenous drug use: Eikonella corrodens
  • Urinary tract infection: Haemophilus
• Sexually-transmitted infection: Neisseria gonorrhoeae
• Medicinal leeches: Aeromonas hydrophila
• Dog or cat exposure: Pasteurella, Bartonella henselae (cats)
• Cattle exposure with prosthetic valve: Coxiella burnetii, Brucella
• Pregnancy: Listeria monocytogenes
• Cirrhosis or chronic alcohol use: Bartonella quintana, Erysipelothrix, Campylobacter, Aeromonas, Pasteurella, Listeria monocytogenes

Investigations

• Blood cultures
  • Routine, modern blood culture incubation will grow almost all easily-cultivable bacteria