VA report 6.12.17: HACEK endocarditis

Case Summary
Thanks to Ashley Stein-Merlob for presenting a fascinating case of a 59M with HFrEF s/p ICD/CRRT p/w fatigue and chills found to have Aggregatibacter bacteremia concerning for infective endocarditis.

Top pearls

  1. In approaching a patient with bacteremia, consider
    • Source of infection (skin, oral flora, GI, GU)
    • Metastatic foci of infection
      • Endocarditis
      • Osteoarticular (osteomyelitis, septic arthritis)
      • Visceral abscess (spleen, liver, kidney)
      • CNS (abscess, mycotic aneursym)
  2. Further divide endocarditis into
    • Acute (staph aureus) versus subacute (other organisms)
    • Native valve versus prosthetic (valve or leads)
  3. Subacute bacterial endocarditis is characterized predominantly by immunologic phenomena
    • Positive rheumatoid factor
    • Glomerulonephritis
    • Splenomegaly, lymphadenopathy
    • Inflammatory back pain.

Infective Endocarditis

To characterize the disease process, endocarditis is further broken down into

  • Acute vs subacute 
    • Acute infective endocarditis is most often caused by Staph aureus, which has the ability to infect undamaged, native valves and presents more abruptly (days).
    • Subacute bacterial endocarditis is caused by less virulent organisms (e.g. strep viridans species) is more likely to involve damaged valves (or prosthetic valves) and  presents subacutely (weeks) with more immunologic phenomenon (see above).
  • Native versus prosthetic valve
    • This distinction influences the microbiology (more coag. negative staph in prosthetic valve disease) and treatment (early surgical intervention in prosthetic valve endocarditis)

Here is a breakdown of the causes of endocarditis:


HACEK organisms

The HACEK organisms have been recently renamed and now include

  • Haemophilus species
  • Aggregatibacter species
  • Cardiobacterium hominis
  • Eikenella corrodens
  • Kingella kingae

These organisms are indigenous flora that colonize the orophaynx and likely play a role in oral infection. They are an infrequent cause of endocarditis (~4%).

Historically, considered as causes of “culture-negative” endocarditis, these organisms are now more easily cultured.

Features of HACEK endocarditis compared to non-HACEK endocarditis:

  • Younger patients (mean 47 vs 61)
  • High prevalence of immunologic manifestations (30% vs 20%)
  • High prevalence of stroke (25% vs 17%)
  • Lower prevalence of CHF (15% vs 30%)
  • Lower in-hospital mortality (4% vs 18%)

More about Aggregatibacter species

  • Accounts for 35% of HACEK infections
  • A positive blood culture represents true bacteremia in 100% of cases
  • File this in your mind as an “abscess-forming organism” which is has propensity for endocarditis, but also causes
    • Periodontal abscess
    • Septic arthritis
    • Osteomyelitis
    • CNS abscess
    • Thyroid abscess



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