HACEK endocarditis is a serious infection affecting the inner lining of the heart. This condition arises when specific types of bacteria, collectively known as HACEK organisms, enter the bloodstream and attach to the heart’s inner surfaces. This bacterial infection can lead to significant damage if not identified and treated promptly.
The HACEK Bacteria
The acronym HACEK represents a group of bacterial genera: Haemophilus, Aggregatibacter, Cardiobacterium, Eikenella, and Kingella. These bacteria are gram-negative and fastidious, meaning they are challenging to grow in laboratory cultures due to their specific nutritional requirements. They are slow-growing, sometimes requiring up to 14 days for detection, and prefer an environment enriched with carbon dioxide.
These organisms are normal inhabitants of the human oral cavity and upper respiratory tract. For instance, Haemophilus parainfluenzae is isolated from dental plaque, and Cardiobacterium hominis is present in the respiratory tract. Aggregatibacter actinomycetemcomitans is linked to periodontal disease, while Kingella kingae often colonizes the throats of young children. Though usually harmless, these bacteria can cause infections, including endocarditis, if they enter the bloodstream.
How Infection Occurs and Who is at Risk
HACEK bacteria enter the bloodstream through breaches in the oral or respiratory mucosa. This can occur during dental procedures, particularly those involving gum manipulation or tooth extraction, or due to poor oral hygiene and existing periodontal disease. They can also enter through other routes such as trauma with wound infections.
Once in the bloodstream, these bacteria adhere to and infect damaged heart valves or prosthetic heart devices. Individuals with pre-existing heart valve abnormalities, such as congenital heart defects, rheumatic heart disease, or prosthetic heart valves, are particularly susceptible. People with compromised immune systems also face an increased risk. The mechanism involves the bacteria forming vegetations, masses of bacteria, platelets, and fibrin, on the heart valves, leading to inflammation and damage to the endocardium.
Recognizing the Symptoms
The symptoms of HACEK endocarditis develop slowly and can be non-specific, making early recognition challenging. Patients commonly experience persistent fever, chills, and fatigue, which can progressively worsen over weeks or months. Other symptoms include night sweats and unexplained weight loss.
A new or changing heart murmur is a common physical sign, indicating potential damage to the heart valves. Less common but more specific signs include splinter hemorrhages (small red or brown streaks under the fingernails), Janeway lesions (painless red spots on the palms or soles), Osler’s nodes (tender red or purple nodules on fingers or toes), and Roth spots (retinal lesions with pale centers).
Diagnosis and Treatment
Diagnosing HACEK endocarditis involves laboratory and imaging tests. Blood cultures are the primary diagnostic tool, though HACEK organisms can be challenging to grow, sometimes requiring extended incubation periods of up to 14 days. Modern automated blood culture systems have improved detection, with some strains growing within an average of 3 to 4 days. If HACEK bacteria are identified in blood cultures without an obvious alternative source of infection, it strongly suggests endocarditis.
Echocardiography is another important diagnostic method, providing images of the heart and its valves. Transthoracic echocardiography (TTE) is usually the initial imaging test, but transesophageal echocardiography (TEE), which offers clearer images by placing a probe down the esophagus, is often used for a more detailed assessment, especially if TTE results are unclear or if prosthetic valves are involved. TEE can visualize vegetations on the heart valves and identify other complications like abscesses or valve damage. Other supportive blood tests, such as inflammatory markers, can also aid in diagnosis.
Treatment for HACEK endocarditis primarily involves prolonged intravenous antibiotic therapy. Ceftriaxone, a third-generation cephalosporin, is a preferred antibiotic due to its broad-spectrum activity against gram-negative bacteria, and it is administered intravenously at a dose of 2 grams every 24 hours. While HACEK organisms were once uniformly susceptible to ampicillin, beta-lactamase-producing strains are becoming more common, making ceftriaxone or other third- or fourth-generation cephalosporins the recommended choice.
Fluoroquinolones may be considered for patients with allergies to beta-lactam antibiotics. The duration of antibiotic treatment is usually 4 weeks for infections involving native heart valves and 6 weeks for those involving prosthetic heart valves. Surgical intervention may be necessary in severe cases, such as when there is significant damage to heart valves, persistent infection despite antibiotic treatment, or the development of complications like heart failure.
Complications and Recovery
HACEK endocarditis can lead to several complications if not managed effectively. Embolic events, where fragments of the infected vegetation break off and travel through the bloodstream, are a concern. These emboli can cause strokes if they reach the brain, or damage other organs such as the kidneys or spleen. Heart failure can also develop due to severe damage to the heart valves, impairing the heart’s ability to pump blood efficiently.
The overall prognosis for HACEK endocarditis is favorable with prompt diagnosis and appropriate treatment. Long-term follow-up care and monitoring are important after successful treatment to ensure complete recovery and detect any late complications. Factors influencing recovery include the extent of valve damage, the presence of pre-existing heart conditions, and the patient’s overall health status.