**2. Epidemiology, pathophysiology, and prophylaxis**

 Bacteremia is a prerequisite for the development of infective endocarditis [1], and it is a more common phenomenon than might be assumed. In fact, transient bacteremia often occurs in various dental and surgical procedures, as well as in toothbrushing, flossing, and even chewing [2]. Despite the ubiquity of transient bacteremia, infective endocarditis is a rare condition with annual incidence in the USA varying between 11 and 15 cases per 100,000 population in the first 12 years of the new millennium [3]. It can thus be surmised that bacteremia alone is insufficient to cause the condition. Data from animal models suggest that the development of IE is dependent on the existence of a valvular lesion, which may be symptomatic, previously unknown or even microscopic, and clinically insignificant. The lesion in turn allows bacteria to adhere to the endocardial surface, promoting the establishment of the principal lesion in infective endocarditis: the vegetation [4].

The degree of valvular damage that is sufficient to cause disease varies greatly depending on the causative agent. *Staphylococcus aureus* has an exceptional status in this regard, owing to its recognized tendency to cause IE in patients without a preexisting valvular condition. Infectious material in the bloodstream causes an upregulation of the body's inflammatory response. Fractions of the vegetation may come loose and cause embolization of other organs. Additionally, the presence of a vegetation on the endocardial surface may contribute irreversible structural damage [3].

The topic of antibiotic prophylaxis to prevent IE is a subject of controversy. As described above, transient bacteremia is very common in the general population,

#### *Infective Endocarditis*

 while manifest infective endocarditis is rare. Concordantly, striving to administer antibiotics to all individuals at risk for transient bacteremia would be a futile endeavor. Indications for prophylaxis in surgical and dental procedures have varied over the years, but it has never been proven that general prophylaxis is indicated, regardless of whether the procedure is high or low risk. Current recommendations, as put forward by the European Society of Cardiology, assert that antibiotic prophylaxis only be considered in high-risk procedures in patients with a pre-existing heart condition that confers a heightened risk of endocarditis. These include prosthetic valve, cyanotic congenital heart disease, and patients with a previous episode of IE. Antibiotic prophylaxis is not recommended in other forms of valvular or congenital heart disease [5].
