Immunocompromised Patients and Health CareAssociated Endocarditis Epidemiology

As medical technology advances, more and more patients have prolonged hospitalizations, are subject to invasive procedures, receive high-dose chemotherapy and corticosteroids, spend more time in intensive care setups and have more central lines, intubations, catheters and other foreign objects inserted. These trends have caused an increase in nosocomial bacteremia and as a result an increase in nosocomial endocarditis.

Cabell et al. [43] studied the demographic and microbiological changes that occurred in patients with infective endocarditis during 1993 to 1999 and their impact on survival. Among the 329 study patients, rates of hemodialysis dependence, immunosuppression and S. aureus infection increased during the study period (P = 0.04, P = 0.008 and P < 0.001, respectively), while rates of infection due to viridans group streptococci decreased (p = 0.007). Hemo-dialysis was independently associated with S. aureus infection (odds ratio, 3.1; 95% confidence interval, 1.6-5.9). Patients with S. aureus endocarditis had a higher one-year mortality rate (43.9% vs. 32.5%; P = 0.04) that persisted after adjustment for other illness severity characteristics (hazard ratio, 1.5; 95% confidence interval, 1.03-2.3). In a recent international study initiated by the International Collaboration for Endocarditis (ICE), healthcare-associated infection was the most common form of S. aureus infective endocarditis. Most patients with health-care-associated S aureus endocarditis (131 patients, 60.1%) acquired the infection outside of the hospital. Persistent bac-teremia was independently associated with MRSA infective endocarditis (OR 6.2; 95% CI 2.9-13.2). Patients in the United States were most likely to be hemodialysis dependent, to have diabetes, to have a presumed intravascular device source, to receive vancomycin, to be infected with MRSA and to have persistent bac-teremia [44].

Mourvillier et al. [45] reviewed charts of 228 consecutive patients admitted to two intensive care units with infective endocarditis between 1993 and 2000. Again, S. aureus emerged as the leading pathogen. The overall in-hospital mortality rate was 45% (102/228). Multivariate analysis revealed the following clinical factors in patients with native valve endocarditis as independently associated with outcome: septic shock (OR 4.81), cerebral emboli (3.00), immunocompromised state (2.88) and cardiac surgery (0.475). Clinical factors in patients with prosthetic valve endocarditis independently associated with outcome were septic shock (4.07), neurological complications (3.1) and immuno-compromised state (3.46).

The increase in nosocomial bacteremia and the related burden of nosocomial endocarditis in newborns is also reflected by the data presented by Opie et al. [46]. In this publication, the incidence of bacterial endocarditis in a level III neonatal nursery was 0.07%. As expected in such young babies the presenting symptoms and signs were often vague and nonspecific. Gestation less than 32 weeks, birth weight less than 1,500 g, thrombocytopenia and neutrope-nia or neutrophilia were common features. The tricuspid valve was involved in seven infants. Of the eight babies six (all of them with tricuspidal endocarditis) had a percutaneous central venous catheter in situ before diagnosis. Mitral valve involvement occurred in two infants, neither of whom had central lines inserted. However, compared to infants without endocarditis, the placement of a central venous line was not of statistical significance.

Nosocomially acquired infective endocarditis carries a worse prognosis compared to infective endocarditis acquired outside in the community. This is due to several reasons: hospitalized patients are usually "sicker," with significant co-morbidities, such as diabetes, renal failure, heart disease, hypertension and malignancies. In addition, many of these patients are immune sup-pressed—whether this reflects their primary disease or is a cause of the treatment they are receiving (e.g., patients receiving chemotherapy). In addition, these patients have a higher rate of S. aureus infective endocarditis, which may cause substantial valvular damage and is harder to cure.

To conclude, in recent years a change in the epidemiology of infective endocarditis has been taking place. The combination of prolonged longevity, the burden of chronic disease and the burden of iatrogenesis have combined to change the features of patients at risk for infectious endocarditis. Thus, the challenge of endocarditis has remained unchanged—timely diagnosis and optimal medical and surgical treatments are still essential for optimal outcome.

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