HACEK ORGANISMS AND THEIR ROLE IN SUBACUTE INFECTIVE ENDOCARDITIS

Abstract

Infective Endocarditis is most commonly caused by gram-positive organisms; however, a small subset of cases is attributed to fastidious gram-negative bacteria known as the HACEK group (Haemophilus spp., Aggregatibacter spp., Cardiobacterium hominis, Eikenella corrodens, and Kingella kingae). These organisms are part of the normal oropharyngeal flora and are characterized by slow growth and specific nutritional requirements, often leading to delayed or initially negative blood cultures. Although rare, HACEK organisms are clinically important causes of subacute infective endocarditis, typically affecting previously damaged heart valves or prosthetic valves. Patients often present with nonspecific symptoms such as prolonged fever, malaise, and new or changing heart murmurs, which can delay diagnosis. Advances in automated blood culture systems have improved detection rates, but prolonged incubation may still be required in some cases. Echocardiography remains essential for identifying valvular vegetations and confirming diagnosis. HACEK-associated endocarditis generally has a favorable prognosis when promptly treated with appropriate intravenous antibiotics, particularly third-generation cephalosporins. This review highlights the microbiological characteristics, clinical presentation, diagnostic challenges, and treatment strategies associated with HACEK group organisms as a rare but significant cause of infective endocarditis.