Although virtually all significant types of infections that occur in the elderly are discussed elsewhere in this book, certain aspects of infectious diseases in older individuals need to be emphasized. This chapter stresses the unique aspects of the etiology and therapy of infections in the elderly (defined here as older than 65 years of age). Infections that occur in longterm care institutions are briefly discussed.

For several reasons, infections in the elderly are an important area of concern for medicine. The number of individuals who are older than 65 is increasing dramatically. Although representing only 13% of the U.S. population at present, the elderly consume 25% of all prescription medications and a similarly disproportionate amount of other health care services. Moreover, with few exceptions (some viral infections and venereal diseases), most common infections occur more often in older individuals.

Although the mortality associated with many infections is increased in the elderly, age alone is now seen as a relatively unimportant risk factor for infection-related death or serious morbidity. Rather, it is the variety of comorbid conditions that are increasingly common with advancing age that appear to be closely associated with greater morbidity and mortality from infection.

Since the early 1990s it has become clear that there is a general hyporesponsiveness of the immune system in elderly individuals. This is the most likely explanation for the muted symptoms and signs that are a common denominator of infections in the aged.