Refers to a grouping of gram-negative bacilli: Haemophilus species (Haemophilus parainfluenzae, Haemophilus aphrophilus, Haemophilus paraphrophilus), Actinobacillus actinomycetemcomitans, Cardiobacterium hominis, Eikenella corrodens, and Kingella species.

These organisms have an enhanced capacity to produce endocardial infections.

HACEK organisms are responsible for approximately 3% of cases of native valve infective endocarditis, and are the most common cause of gram-negative endocarditis among persons who do not abuse intravenous drugs.

The HACEK organisms (Haemophilus, Actinobacillus actinomycetemcomitans, Cardiobacterium hominis, Eikenella corrodens, Kingella) 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.

These organisms are part of the normal human oral flora.

They have a fastidious and slow growth.

Often a cause of culture-negative endocarditis.

Aside from cardiac valve infections this group of agents may be associated with periodontal infections, abscesses, peritonitis, otitis media, conjunctivitis, pneumonia, septic arthritis, osteomyelitis, urinary tract infections, wound infections, and brain abscess.

These bacteria have the potential for abscess formation and invasive disease.

May produce vegetations on infected cardiac valves that are complicated by macroemboli.

Sixty percent of cases of HACEK infectious endocarditis associated with dental disease.

Haemophilus species are pleomorphic gram-negative coccobacilli that require X (hemin) and/or V (nicotinamide adenine dinucleotide) factors found in red blood cells for isolation.

Haemophilus species are responsible for 0.5%-1% of all cases of infectious endocarditis, and 40% of those are due to H aphrophilus, followed by H parainfluenzae.

Ten percent of cases of Heamophilus species infectious endocarditis involve a second pathogen, usually an alpha-hemolytic Streptococcus or Staphylococcus aureus.

Endocarditis due to H parainfluenzae has been increasing in frequency, with 45% associated with oral pathology and 10% are associated with upper respiratory tract infections.

In Heamophilus species infectious endocarditis the mitral valve involved 67% of cases and in 17% the aortic valve is involved.

In Heamophilus species infectious endocarditis fifty percent of patients have underlying valvular disease.

Actinobaccilus actinomycetemcomitans is the etiologic agent of localized juvenile periodontiti, and when involved with infectious endocarditis 86% have underlying heart disease and 25% have infection of a prosthetic valve ,usually aortic.

Cardiobacterium homonis is part of the normal flora of the mouth and upper airway and can be found in the large bowel.

C.homonis infectious endocarditis usually secondary to oral pathology.

Eikinella corrodens is a facultatively anaerobic organism that is part of the oral flora and many other mucosal surfaces.

E corrodens is usually isolated with other organisms, especially streptococci and is a common cause of cellulitis resulting from human bites, soft-tissue infections and endocarditis in drug abusers, pulmonary infections, and infections are often complicated by osteomyelitis.

E corrodens infectious endocarditis usually associated with valve lesions and intraveous drug abuse.

Kingella species include Kingella kingae, Kingella denitrificans, and Kingella indologenes.

K kingae is the usual cause of infectious endocarditis among these organsims.

HACEK organisms were found to be responsible for more than half of endocarditis cases due to gram-negative organisms in the past.

Patients with endocarditis caused by the HACEK organisms usually have subacute illness, with the exception of H parainfluenzae endocarditis, which may present more acutely.

Large valvular vegetations and increased peripheral embolization are common.

Mortality rate approximately 10-15%.

No apparent racial or sexual predominance but more common in older individuals.

Progressive symptoms developing over weeks and some cases take many months to diagnosis due to failure to use special culture techniques.

HACEK infectious endocarditis should be considered in the differential diagnoses of fever of unknown origin.

Fever is common but may be absent in elderly individuals and immunocompromised patients.

Nonspecific symptoms are common and may lead to a delay in diagnosis.

History of prior valvular disease, prior dental, urologic, and other procedures should be noted, along with intravenous drug use.

Special lab testing of blood cultures increase cahnces of isolating the organism, and prolonged incubation of the specimen is recommended.


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