HACEK Group Infections Workup

Updated: Jun 17, 2016
  • Author: Zartash Zafar Khan, MD, FACP; Chief Editor: Burke A Cunha, MD  more...
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Workup

Laboratory Studies

When a HACEK organism is suspected, consider consulting a microbiologist so that special attention can be given to the blood culture specimen. Special procedures performed in the microbiology laboratory my improve the chances of isolating the organisms. [13]

Although prolonged incubation is commonly recommended in this setting, current research suggests it is the special laboratory procedures, rather than the time of incubation, that matter most. [13]

Molecular techniques for the detection and identification of microorganisms have been increasingly used for diagnostics in clinical microbiology. Polymerase chain reaction (PCR) of the 16S rRNA genes and sequencing has increased diagnostic yield, although diagnostic sensitivity is difficult to be determined at this time. [23]

Complete cell count may show anemia with or without reactive thrombocytosis. Total white cell count may or may not be increased.

Other inflammatory parameters should include erythrocyte sedimentation rate and C-reactive protein, although these are nonspecific. 

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Imaging Studies

Echocardiography

Echocardiography plays an important role in the diagnosis and management of endocarditis. Characteristic vegetations, abscesses, new prosthetic-valve dehiscence, or new regurgitant murmur are 4 powerful identifiers of infective endocarditis (IE) (in combination with other clinical criteria).

Transthoracic echocardiography (TTE) has the advantages of being fast and easy to perform. Specificity for vegetations is 98%; however, sensitivity is lower than 60%. TTE views may be inadequate in approximately 20% of the adult population because of obesity, chronic obstructive pulmonary disease, or chest-wall deformities. TTE cannot exclude infection of prosthetic valves, periannular abscess, leaflet perforation, or fistulae.

Transesophageal echocardiography has the advantage of having higher sensitivity for vegetations and greater specificity and sensitivity for perivalvular extension than TTE.

HACEK group organisms typically produce vegetations that are larger than vegetations found in IE due to other organisms, probably because of the longer mean time to diagnosis.

In addition to its diagnostic utility, echocardiography may play a prognostic role. Certain vegetation characteristics are associated with increased risk for embolism and mortality. [24]

CT scanning

CT scanning can be used for diagnosis of soft-tissue or visceral abscess.

MRI

MRI is more sensitive and specific for bone infection. 

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Procedures

The most common presentation of HACEK endocarditis is an indolent or subacute endocarditis that is cured with an appropriate course of intravenous antibiotics. In cases of less-common acute clinical presentation with perivalvular abscess and rapid hemodynamic deterioration with heart failure, valve replacement may be necessary. [25]

An arterial embolectomy for large emboli may be needed to salvage a limb or viscera.

Surgical interventions such as incision and drainage or abscess evacuation may be needed if clinically prompted. 

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Histologic Findings

The valvular lesions and vegetations of HACEK IE are very similar to those found in other types of subacute endocarditis, except that the larger size of the vegetations resembles those seen in fungal or staphylococcal disease. [26, 27]

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