Infective endocarditis has become more prevalent in the elderly de¬spite the development of modern antibiotics. More than half of all cases of infective endocarditis occur in persons >60yrof age. Several factors account for the high prevalence in the elderly: increases in the total number of elderly persons and in the number with prosthetic valves, a higher prevalence of hospital-acquired bacteremia, longer survival o\’ persons with rheumatic valvular lesions, and fewer new cases of rheu¬matic heart disease.
Etiology
The underlying cardiac lesions that predispose Ihe elderly to endocar¬ditis lend to differ from those in younger patients. The increased inci¬dence of atherosclerosis in the elderly may be a factor, since atheroma-

tous deposits can cause turbulence and. hence, thrombus formation. All forms of valvular disease increase the risk of endocarditis, although about 40% of elderly patients with endocarditis have either no valvular lesions or undetermined ones. Of the 60% who do have valvular dis¬ease, about 30% have rheumatic lesions, about 25% have calcified valves, and about 5% have mitral valve prolapse (see Ch. 38).
The aortic valve is involved in 20% to 40% of cases. The high inci¬dence of aortic valve involvement probably reflects the increased prev¬alence of aortic stenosis with calcification in Ihe elderly. Until age 60. aortic stenosis with calcification is most commonly caused by rheu¬matic heart disease; from age 60 to 75, a calcified congenital bicuspid valve is most often implicated; and after age 75, degeneration of a nor¬mal valve is the leading cause. The mitral valve is involved in 25% to 70% of endocarditis cases, and both the aortic and mitral valves are involved in about 10% to 25%. Infections involving congenital heart de¬fects other than those of Ihe bicuspid valve occur infrequently in the elderly.
The development of infective endocarditis involves 1 wo events. First is an alteration in the endocardial surface, which then permits the deposi-lion of platelets and fibrin. The resulting thrombus or vegetation most often arises in areas of increased turbulence. Second is transient bacter¬emia, which allows the thrombus to be colonized. The source of bacter¬emia is usually unknown. Sites of primary infection include the mouth, the GU tract (particularly afler procedures involving instrumentation), the GI tract, skin and decubitus ulcers, surgical wounds, and IV cath¬eters.
Bacterial properties—eg. the increased adherence of certain strepto¬coccal and staphylococcal species—-make some organisms more likely than others to cause infective endocarditis. Streptococcus spp are the most common, accounting for 25% to 70% of endocarditis cases, al-Ihough the viridans streptococci arc less prevalent in older than in younger populations. Enterococci, which often inhabit the GU and lower Gl tracts, can account for up to 25%’ of endocarditis cases in el¬derly men. Frequent urinary tract infections and procedures involving instrumentation (especially in men wilh prostate disease) explain the increased frequency of enterococcal bacteremia and endocarditis. S. bovis, a nonenterococcal group D streptococcus, can be isolated in up to 25% of endocarditis cases in persons > 55 yr. Many such cases are associated with underlying and often asymptomatic malignant or premalignant GI lesions, especially colon carcinoma.
Staphylococci account for 20% to 30% of all endocarditis cases in the elderly. The predominant species. Staphylococcus aureus, often causes nosocomial endocarditis, and many cases are discovered only incidentally at autopsy. 5- ep’tdermidis is isolated in < 5% of cases of native valve endocarditis, but in elderly as in younger patients, it is the most common single cause of cases involving prosthetic valves.