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Q1: What are the most common organisms causing artificial valve endocarditis? What are other less common organisms should be considered?
The most common aetiological organism isStaphylococcus epidermidis which accounts for 29% of both early and late onset endocarditis, followed by viridans streptococci (17%),Staphylococcus aureus (14%), and enterococci (7%).1 Aerobic Gram negative bacilli, diphtheroids including corynebacterium Jeikeium, and fungi especially candida and asperigillus species uncommon in native valve endocarditis are important causes of early prosthetic valve endocarditis.1
Less common organisms include Coxiella burnetii, Brucella spp, and the HACEK group.1
Q2: How should the diagnosis be established?
Relapsing brucella bacteraemia after appropriate treatment for acute brucellosis is an important clue for the diagnosis of brucella endocarditis in patients who have prosthetic valves.2 An epidemiological and exposure history is essential and usually helpful in the diagnosis. Our patient was a farmer who kept animals like goats in his farm. Diagnosis depends on isolation of brucella from blood culture and/or cardiac tissues. Serology is also helpful. The standard tube agglutination test is sensitive and specific. A titre of 1:160 or more is presumptive evidence of brucella infection. Echocardiography especially transoesophageal echocardiography may be useful in detecting vegetations, prosthesis detachment, and perivalvular abscess. Other indications include anaemia, haematuria, and a high ESR.
Q3: What would be the best therapeutic approach?
Treatment for brucella endocarditis has not been well established, due basically to the low number of reported cases. Brucella organisms are susceptible to a variety of antibiotics including aminoglycosides, tetracyclines, chloramphenicol, quinolones, macrolides, rifampin, and trimethoprim-sulfamethoxazole (TMP-SMZ).3 Most patients with brucella endocarditis are treated with combination antibiotics including tetracycline, streptomycin, rifampin, and/or TMP-SMZ. The best combination of antibiotics is not known. Some authors suggested a combination of doxycycline, rifampin, and streptomycin,3however the interference of rifampin with the anticoagulant activity of warfarin and related drugs, and the inconvenience of intramuscular streptomycin injection makes this combination less attractive. Prosthetic valve endocarditis caused by brucella is a primary indication for surgery4; it has never been cured with antibiotics alone. All reported patients had combined medical and surgical treatment. Our patient underwent valve replacement four days after the start of antibiotic treatment. The optimal duration of antimicrobial therapy for brucella endocarditis is unknown. However it seems advisable to extend antibiotic treatment for a minimum of 12 weeks postoperatively. A progressive drop in antibody titre, and a negative mercaptoethanol titre, points toward a bacteriological cure; patients who have a relapse or fail treatment persist with high concentrations of IgG resistant to mercaptoethanol.4
Brucellosis is a zoonosis with a worldwide distribution, especially in the Mediterranean basin, the Arabian Peninsula, the Indian subcontinent, Mexico, Central and South America.2It is a systemic disease, and almost every organ can be affected. The infection usually manifests itself as a febrile syndrome with no apparent focus, chills, sweating, arthralgia, and myalgia. About 30% of patients suffer from some localisation, most commonly bone and joint involvement.1 Brucella endocarditis is rare occurring in fewer than 2% of patients with brucellosis.1 Prosthetic valve endocarditis caused by brucella species is very rare.Brucella abortus, B suis, andB melitensis have been reported to cause endocarditis. Brucella endocarditis produces highly destructive lesions of the valve structure.5 It usually involves a previously healthy native valve. The aortic valve is involved in more than 75% of cases. Mitral involvement occurs more rarely and usually affects a previously damaged valve.5 The valvular lesions have been described as bulky and ulcerative with gross abscesses of the myocardium, microabscesses within the cusps, destruction of commissures, and calcifications.6 These observations might explain the high fatality rate for brucella endocarditis. Although the mortality rate for brucellosis is less than 1%, endocarditis accounts for 80% of these deaths.6 The complication, which is responsible for the majority of deaths, is heart failure.6Major systemic emboli in contrast to other causes of prosthetic valve endocarditis were rare; this has been attributed to the tendency of infection to cause fibrosis, hyalinisation, and calcification, rather than large vegetations.2 6 Diagnosis depend on isolation of brucella from blood culture or cardiac tissue, which are positive in 80% of cases. Combined antibiotic and surgical treatment is the best approach for treating brucella prosthetic valve endocarditis as the mortality rate is less than for medical treatment alone, and infection of the new prosthesis that has been placed is low.1
Brucella prosthetic valve endocarditis.