Schlossberg : Current Therapy of Infectious Disease - HACEK

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Current Therapy of Infectious Disease

David Schlossberg

PART 5:

SPECIFIC PATHOGENS AND INFECTIONS
Bacteria

133	HACEK Christopher H. Cabell · Daniel J. Sexton

The acronym HACEK describes a heterogeneous group of organisms that share two major characteristics. First, they are fastidious gram-negative rods that require forethought and special measures to culture in the microbiology laboratory. Second, they have a predilection to infect heart valves. The HACEK group includes Haemophilus species (except H. influenzae), Actinobacillus actinomycetemcomitans, Cardiobacterium hominus, Eikenella corrodens, andKingella species. These organisms are infamous for their ability to cause endocarditis although, rarely, they cause a variety of other infections (Table 1). For example, human bites can result in cellulitis or abscess formation resulting from HACEK organisms, especially Eikenella species, and various Haemophilus species can cause epiglottitis or brain abscesses.

Table 1 HACEK-Associated Infections
Haemophilus aphrophilus haemolyticus parahaemolyticus parainfluenzae paraphrophilus segnis	Brain abscess, endocarditis, endophthalmitis, epiglottitis, hepatic abscess, intraabdominal infection, meningitis, neonatal sepsis, necrotizing fascitis, otitis media, pneumonia, sinusitis, septic arthritis, urinary tract infection
Actinobacillus actinomycetemcomitans	Brain abscess, cellulitis, empyema, endocarditis, endophthalmitis, osteomyelitis, periodontal infection, parotitis, pericarditis, pneumonia, synovitis, thyroid abscess, urinary tract infection
Cardiobacterium hominis	Endocarditis, meningitis
Eikenella corrodens	Abscessed tooth, Bartholin's gland abscess, brain abscess, cellulitis, conjunctivitis, dacryocystitis, empyema, endocarditis, endometritis, gingivitis, intraabdominal abscess, intravascular space infections, keratitis, liver abscess, mediastinitis, meningitis, mycotic aneurysm, otitis externa, parotitis, pericarditis, pneumonia, septic pulmonary emboli, subdural empyema, thyroid abscess, thyroiditis
Kingella dentrificens indologenes kingae	Abscess, endocarditis, epiglottitis, intervertebral diskitis, meningitis, oropharyngeal infections, osteomyelitis, septic arthritis

Members of the HACEK group are normal indigenous flora of the oral cavity. Systemic hematogenous spread may occur after dental manipulation or secondary to periodontal disease. Thereafter, individuals with underlying valvular heart disease are at risk of developing endocarditis. Antibiotic prophylaxis before dental manipulation does not ensure complete prevention against these fastidious organisms. However, the risk of endocarditis is very small after dental manipulation, even in patients with significant valvular disease. Millions of patients undergo dental procedures annually, yet the cases of infective endocarditis (IE) caused by HACEK group organisms are rare.

DIAGNOSIS

The key to the diagnosis of HACEK infections is suspicion by the treating physician. Without proper information, the microbiology laboratory may not take necessary steps to culture these organisms. Most laboratories routinely discard blood culture bottles after 7 days. Many members of the HACEK group may not be detectable in culture bottles after a week of incubation. To detect HACEK group organisms, blood cultures must be subcultured onto agar plates, which are incubated for an additional 2 to 3 weeks. HACEK organisms typically grow on 5% sheep blood and chocolate agar but not on MacConkey's agar. Because growth is often poor or absent in an unenhanced atmosphere, incubation in 5% to 10% carbon dioxide (CO₂) is recommended. After growth is observed, standard biochemical tests will identify individual HACEK species.