HACEK endocarditis

A HACEK organism is one of a set of slow-growing Gram negative bacteria that form a normal part of the human flora.

They are a frequent cause of endocarditis in children^[1], but affect adults too.

Organisms

The name is formed from their initials:^[2]

• Haemophilus (Haemophilus parainfluenzae, Haemophilus aphrophilus, Haemophilus paraphrophilus)^[3]
• Actinobacillus (Actinobacillus actinomycetemcomitans, Aggregatibacter aphrophilus^[4])
• Cardiobacterium hominis
• Eikenella corrodens
• Kingella (Kingella kingae)

Presentation

All of these organisms are part of the normal oropharyngeal flora, which grow slowly, prefer a carbon dioxide–enriched atmosphere, and share an enhanced capacity to produce endocardial infections, especially in young children. Collectivelly they account for 5-10% of cases of infective endocarditis involving native valves and are the most common gram-negative cause of endocarditis among people who do not use IV drugs. They have been a frequent cause of culture-negative endocarditis. Culture negative refers to an inability to produce a colony on regular agar plates; this is because these bacteria are fastidious (require a specific nutrient).

In addition to valvular infections in the heart, they can also produce other infections such as bacteremia, abscess, peritonitis, otitis media, conjunctivitis, pneumonia, arthritis and osteomyelitis, and periodontal infections.

Treatment

The treatment of choice for HACEK organisms in endocarditis is ceftriaxone, a third generation cephalosporin (penicillin-based) antibiotic. Ampicillin (a penicillin) and low-dose gentamicin (an aminoglycoside) is another therapeutic option.^[5]

References

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