The impact of infectious diseases on older adults is far greater than on younger adults because of significantly higher morbidity and mortality caused by infection. The reasons for this greater impact include factors such as lower physiologic reserve due to age and chronic disease, age-related changes in host defenses, loss of mobility, higher risk for polypharmacy and adverse drug reactions, and being on drugs that increase the risk for infection (e.g., anticholinergic and other sedating medications increase the risk for pneumonia).