The HACEK organisms, or HACEK group, is an acronym for Haemophilus spp., Aggregatibacter spp., Cardiobacterium hominis, Eikenella corrodens, and Kingella kingae, a group of Gram-negative common oral commensal bacteria which are associated with infective endocarditis.
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Epidemiology
Infective endocarditis is usually caused by Staphylococcus or Streptococcus Gram-positive bacteria, with only 1.4-6% of cases attributable to HACEK organisms 1,7,8. Infective endocarditis more broadly has a male-to-female ratio of 2:1 2,3. Those who are infected by HACEK organisms tend to be slightly younger (median 47 years old) than those infected by other organisms (median 61 years) 1.
Kingella kingae, one of the HACEK organisms, is also frequently implicated in pediatric bone and joint infections, being the main cause of osteomyelitis and septic arthritis for children aged 6 months to 3 years 8,9.
Clinical presentation
Osler nodes (red-purple tender subcutaneous nodules on the fingers and toes) are more common in HACEK related bacterial endocarditis, which is also more commonly associated with mechanical heart valves, and vascular immunologic phenomena 1-3. Diabetes mellitus is a risk factor for infective endocarditis, but is more often associated with non-HACEK infection 1,3.
Pathology
HACEK organisms are usually asymptomatic oropharyngeal commensal bacteria, which can cause infection through hematologic spread to the heart (endocarditis), bone (septic arthritis and osteomyelitis), and central nervous system (abscess, meningitis) 1,9.
Treatment and prognosis
Treatment for infective endocarditis often includes a second agent for HACEK organism coverage such as ceftriaxone 4. The duration of treatment may be shortened to 4 weeks in confirmed HACEK infection or extended to 6 weeks with prosthetic valve involvement, although the evidence for this is limited 4. There are ongoing clinical trials evaluating shorter treatment durations for infective endocarditis 5,6.
A national cohort study found that infective endocarditis caused by HACEK organisms had a better outcome than that caused by non-HACEK organisms (3% in-hospital mortality compared with 18%) 1. The incidence of stroke, particularly hemorrhagic stroke, is higher in cases of infective endocarditis caused by HACEK organisms, which notably affects a slightly younger demographic, and increases hospital stay by ~20 days 1.
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