Recognition, management and prophylaxis of endocarditis

Uncommon pathogens causing infective endocarditis

Infective endocarditis is caused by a wide range of aetiological agents. The microbiology, epidemiology, and treatment of this disease have changed considerably in the last two decades. Staphylococci and streptococci are known to be the classical causative agents; however, blood culture-negative endocarditis caused by fastidious and slow-growing organisms is now common. The list of uncommon pathogens causing endocarditis has expanded in recent years. This is a narrative literature review of the aetiological agents of endocarditis that are rarely encountered in clinical practice, their epidemiology, the characteristics of these pathogens, the clinical presentations of the cases, and their management.

Infective Endocarditis and Phlebotomies May Have Killed Mozart

Thirty-five year-old Amadeus Mozart died in Vienna after an acute illness that lasted only 15 days but no consensus has been reached on the cause of his death. From many letters written by his farther it is almost certain that he experienced at least three episodes of acute rheumatic fever attack in his childhood, and a relapse of rheumatic fever was suggested to have killed Mozart, although death from acute rheumatic fever is very rare in adults. His last illness was characterized by high fever, massive edema, vomiting and skin rash. His last illness can be explained by infectious endocarditis and heart failure. During his last hours, he was given phlebotomy, possibly for the third time in two weeks, and soon after he became unconscious and died. As such, phlebotomy performed on a man dehydrated by high fever and vomiting may have caused systemic shock. In summary, Mozart probably died from chronic rheumatic heart disease complicated by infective endocarditis and heart failure, and repeated phlebotomy-induced hypovolemic shock.

New insight into the diagnosis of fastidious bacterial endocarditis

Sterile blood cultures are noted in one third of patients with infectious endocarditis. Although in half of cases this is due to previous antibiotic therapy, in the other half, the aetiology of culture-negative endocarditis is intracellular bacteria such as Coxiella burnetii or fastidious growing bacteria. Although it was previously considered that the prevalence of such organisms was identical throughout the world, recent investigations on Bartonella endocarditis clearly showed that the aetiology of culture-negative endocarditis is likely to be strongly related to epidemiology of the agent in each country. During the past decade the use of molecular techniques such as PCR with subsequent sequencing to detect or to identify bacteria in valves from patients with infectious endocarditis have considerably improved the aetiological diagnosis. This is especially true in the case of culture-negative endocarditis following earlier antibiotic therapy. However, the fact that DNA remnants of past endocarditis can be detected some time after the acute episode, when the patient has been cured, suggests that the predictive value of these techniques along with the traditional histology and culture need to be evaluated closely.

Clinical features remain important for the diagnosis of infective endocarditis in the modern era

BACKGROUND

Infective endocarditis (IE) can be difficult to diagnose, due to multiple (often non-specific) presenting features.

AIM

To assess the predictive accuracy of classical clinical features and blood investigations readily available at the time of presentation.

DESIGN

Cross-sectional analysis.

METHODS

We studied 29 IE cases and 79 controls (clinically suspicious contemporaneous cases where IE was subsequently excluded) from a hospital-based group of patients referred to a cardiac department with possible infective endocarditis. Patients were identified from the echocardiography database. Cases were defined by final diagnosis. Symptoms, signs, risk factors for IE and blood investigations were recorded from case notes and examined by univariate and multivariate analyses.

RESULTS

The sensitivity, specificity, and positive and negative predictive values of transthoracic echocardiography (TTE) for detection of IE in clinically suspected cases were 71%, 98%, 57% and 99%, respectively. Univariate analyses revealed a significant association between IE and several clinical features. Under multivariate analysis, previous heart valve surgery (OR 13.3, 90%CI 3.2-55.6), positive blood cultures (OR 17.2, 90%CI 4.9-58.8), signs of embolism (OR 11.4, 90%CI 3.0-43.5), a new, altered or changing murmur (OR 10.3, 90%CI 2.8-38.5) and splenomegaly (OR 18.2, 90%CI 3.6-90.9) were independent predictors for IE.

DISCUSSION

Clinical features at presentation continue to be important for the diagnosis of IE. Features such as positive blood cultures, signs of embolism and a changing heart murmur should be used to guide investigation and treatment of IE prior to echocardiography, or when TTE is negative.

Optimisation of the prevention and treatment of bacterial endocarditis

This paper reviews currently established guidelines for the prevention and treatment of bacterial endocarditis. Endocarditis remains a life-threatening disease with substantial morbidity and mortality. Primary prevention of endocarditis, whenever possible, is therefore very important. In an individual with endocarditis, rapid diagnosis and effective treatment are essential to good patient outcome. The guidelines discussed here are largely based on those issued by the American Heart Association. While most cases of endocarditis are not attributable to an invasive procedure, certain procedures are associated with bacteraemia by organisms commonly associated with endocarditis, and antibacterial prophylaxis is recommended before such procedures. Patient cardiac conditions are stratified into high, moderate and negligible risk categories based on potential outcome if endocarditis develops. For oral, dental, respiratory tract, and oesophageal procedures (most often associated with viridans streptococci) the standard antibacterial regimen is oral amoxicillin. For gastrointestinal and genitourinary procedures (most often associated with enterococci), parenteral antibacterials are most often recommended. For high-risk patients, intramuscular or intravenous ampicillin and gentamicin (or vancomycin and gentamicin in penicillin-allergic individuals) is recommended. For moderate risk patients, an option of oral amoxicillin or parenteral ampicillin is offered. Treatment of bacterial endocarditis is guided by identification of the causative micro-organism. Approximately 80% of cases of endocarditis are due to the gram-positive cocci: streptococci and staphylococci. Other gram-positive organisms include enterococci (predominantly Enterococcusfaecalis and E. faecium) and the HACEK group of organisms (Haemophilus parainfluenzae, H. aphrophilus, Actinobacillus [Haemophilus] actinomycetemcomitans, Cardiobacterium hominis, Eikenella corrodens, and Kingella kingae). In general, for uncomplicated cases of endocarditis due to penicillin-susceptible viridans streptococci or Streptococcus bovis 4 weeks of benzylpenicillin (or ceftriaxone) is the preferred regimen for most patients aged >65 years. A 2-week course of treatment can be used when gentamicin is added, in patients at low risk for adverse events caused by gentamicin therapy. When endocarditis is caused by strains of viridans streptococci or S. bovis relatively resistant to penicillin, or by enterococci, both benzylpenicillin and gentamicin are recommended. For staphylococcal endocarditis on native heart valves, nafcillin or oxacillin with or without gentamicin is the preferred regimen. In prosthetic valve staphylococcal endocarditis, nafcillin (or oxacillin) with rifampicin and gentamicin is recommended. For all of the above situations, vancomycin is recommended for the patient allergic to penicillin (or methicillin). Finally, consideration of out-of-hospital therapy in selected patients is discussed.

Concepts for the prophylaxis of infective endocarditis in dentistry

Oral commensal microorganisms are commonly associated with the pathogenesis of infective endocarditis. Despite modern antimicrobial and surgical treatment, infective endocarditis continues to cause substantial morbidity and mortality. Although dentistry is no longer considered a major risk factor for infective endocarditis, it is current standard for practice that dental procedures likely to produce significant bacteraemia in patients who are susceptible to this disease be prophylactically covered with an antimicrobial agent. The concepts of antimicrobial prophylaxis prior to invasive dental procedures are outlined in this review, with particular reference to the latest recommendations of the Australian Dental Association.

A retrospective review of 228 episodes of infective endocarditis where rheumatic valvular disease is still common

Two hundred and twenty-eight episodes of infective endocarditis in adult patients (mean age 36 years) were reviewed retrospectively. There were 183 episodes (80%) of native valve, 15 (7%) early prosthetic valve and 30 (13%) late prosthetic valve endocarditis. The most common predisposing factor was rheumatic valvular disease (65%). None of the patients were intravenous drug users. According to the Duke criteria, the number of definite, probable and rejected episodes were 121 (53%), 94 (41%) and 13 (6%), respectively. Additional minor criteria increased the number of definite endocarditis to 82%. The Duke criteria are not primarily intended to influence treatment decisions but are helpful in standardising research activities. The choice of the level of sensitivity or specificity of the criteria may be adjusted according to the aim of the study and prevalence of disease in a particular area. More sensitive criteria may be valuable in those countries where the prevalence of rheumatic valvular disease is still high.

Endocarditis due to rare and fastidious bacteria

The etiologic diagnosis of infective endocarditis is easily made in the presence of continuous bacteremia with gram-positive cocci. However, the blood culture may contain a bacterium rarely associated with endocarditis, such as Lactobacillus spp., Klebsiella spp., or nontoxigenic Corynebacterium, Salmonella, Gemella, Campylobacter, Aeromonas, Yersinia, Nocardia, Pasteurella, Listeria, or Erysipelothrix spp., that requires further investigation to establish the relationship with endocarditis, or the blood culture may be uninformative despite a supportive clinical evaluation. In the latter case, the etiologic agents are either fastidious extracellular or intracellular bacteria. Fastidious extracellular bacteria such as Abiotrophia, HACEK group bacteria, Clostridium, Brucella, Legionella, Mycobacterium, and Bartonella spp. need supplemented media, prolonged incubation time, and special culture conditions. Intracellular bacteria such as Coxiella burnetii cannot be isolated routinely. The two most prevalent etiologic agents of culture-negative endocarditis are C. burnetti and Bartonella spp. Their diagnosis is usually carried out serologically. A systemic pathologic examination of excised heart valves including periodic acid-Schiff (PAS) staining and molecular methods has allowed the identification of Whipple's bacillus endocarditis. Pathologic examination of the valve using special staining, such as Warthin-Starry, Gimenez, and PAS, and broad-spectrum PCR should be performed systematically when no etiologic diagnosis is evident through routine laboratory evaluation.

Differential diagnosis of infective endocarditis

Infective endocarditis (IE) is a deadly disease if left untreated. Early detection and treatment of IE reduces the high mortality rate. Mitral valve prolapse is now the leading risk factor for development of IE. The Duke (1994) criteria includes echocardiography as a diagnostic tool. Outclient i.v. therapy is increasing due to once-daily dosing regimens, which reduces the cost of treatment. Identifying at risk clients and educating them is vital to the prevention of IE. This article familiarizes the primary care provider with the pathophysiology, clinical presentation, diagnostic testing, complications, medical treatment, prophylactic management, and client education of IE.

Outpatient intravenous antibiotic therapy for endocarditis

The clinical spectrum of endocarditis continues to evolve, as does its diagnosis and management. Outpatient parenteral antimicrobial therapy has been demonstrated to be safe and effective for medically stable patients with viridans streptococcal endocarditis. Other carefully selected and monitored patients with infective endocarditis may also be considered for completion of therapy outside the hospital setting.