Microbiology

The HACEK group consists of fastidious, slow-growing, gram-negative bacteria whose growth requires carbon dioxide. Several Haemophilus spp., Aggregatibacter (formerly Actinobacillus) actinomycetemcomitans, Aggregatibacter (formerly Haemophilus) aphrophilus, Cardiobacterium hominis, Eikenella corrodens, and Kingella kingae make up this group. Normal residents of the oral cavity, HACEK bacteria can cause both local oral infections and severe systemic disease, particularly endocarditis.

Clinical Manifestations

• HACEK organisms caused 0.8-6% of cases of infective endocarditis; most of these cases are due to Aggregactibacter spp., Haemophilus spp., or C. hominis.
• Infection typically occurs in pts with underlying valvular disease, often in the setting of a recent dental procedure or nasopharyngeal infection.
• The aortic and mitral valves are most commonly affected. Aggregatibacter and Haemophilus spp. cause mitral valve vegetations most often, while C. hominis is associated with aortic valve vegetations.
• Embolization is common, with 28-71% of pts affected.
• H. parainfluenzae is the most common Haemophilus species isolated in cases of HACEK endocarditis. Pts usually present within the first 2 months of illness, and 19-50% of pts develop CHF.
• Aggregatibacter spp. are the most common cause of HACEK endocarditis and cause prosthestic-valve endocarditis more often than Haemophilus spp. A. actinomycetemcomitans is isolated from soft-tissue infections in association with Actinomyces israelii. Pts with Aggregatibacter endocarditis often have periodontal disease or have recently had dental work and are sick for several months before diagnosis.
• C. hominis typically causes endocarditis in pts with valvular heart disease or prosthetic valves. Long-standing infection with systemic manifestations usually precedes diagnosis. A second species, C. valvarum, has been described in association with endocarditis.
• E. corrodens is usually a component of mixed infections and is common in human bite wounds, head and neck soft-tissue infections, endocarditis, and infections in IV drug users.
• K. kingae is a common cause of musculoskeletal infections in children <4 years old. Inoculation of clinical specimens (e.g., synovial fluid) into aerobic blood-culture bottles enhances recovery of this organism. Infective endocarditis due to K. kingae occurs in older children and adults with preexisting valvular disease.