2. Epidemiology

There has been a significant increase in the overall incidence of infectious endocarditis—and there are many reasons for this. The two, probably, most important fundamental reasons are the growing number of patients with substantial comorbidities who are receiving therapies involving prosthetic material implanted into their hearts. Many of these patients have comorbidities that historically might have contraindicated advanced cardiac therapies (including heart valve surgery) years ago. Such comorbidities included not only frailty and advanced age but end-stage renal disease, history of solid or bone marrow transplantation, chronic highintensity immunosuppression, and multiple previous cardiac procedures. In addition, the fact that medical advances have resulted in these "sick" patients living longer, even if the absolute rate (i.e., cases/year) did not change, the total number of cases would increase as the overall population at risk over time has increased.

The second growing population of patients at risk for developing endocarditis are patients with a history of intravenous substance abuse—and even more so, those who continue to abuse IV drugs having already undergone a surgical procedure to repair/replace an infected cardiac valve [3, 4]. The global burden of substance abuse and the impact of infectious endocarditis are only recently been the sources of focused investigation with a growing appreciation of the magnitude of the problem [5]. Many of these patients tend to be younger—and as a function of their greater physiologic reserve, difficulties in getting appropriate access to healthcare and the means in which they become infected can result in this population presenting much later in the course of an infection with advanced cardiac structural destruction and are more likely to have polymicrobial or fungal infections. As many of these patients have received suboptimal therapy for their nonspecific presentations and symptoms, late presentations after weeks, or even months, of therapies for "viral syndromes," "community acquired pneumonias," or even "cellulitis" from local infections at the site of infection are not uncommon. Noncompliance with medical therapy, combined with mistrust in the healthcare system, in this population might also predispose them to presenting late in their disease. Nevertheless, as more patients receive advanced cardiac therapies—such as catheter-based valve replacements, implantable cardioverter defibrillators, pacemakers, intravascular remote pressure monitors, and ventricular assist devices—the risks for developing device-related infections are substantial and growing [6, 7]. Unfortunately, the growth in the overall utilization of these devices in sicker patients has exceeded our overall understanding of how to reduce, prevent, or provide prophylaxis against potential infections [8–10]. Furthermore, with the growing understanding of the natural history of endocarditis, risk factors for developing infections, the management of specific types of infections and their presenting complication, long-term outcomes of both medical and surgical therapies, and the overall heterogeneous spectrum of clinical presentation, medical and surgical teams are becoming better at individualizing care plans.
