IMMUNE FUNCTION

An overall decline in immune system capabilities with aging can pose an increased risk for some infections (see Chapter 19). Involution of the thymus gland is com­plete by approximately 45 to 50 years of age, and although the total number of T cells remains unchanged, there are changes in the function of helper T cells that alter the cellular immune response of older adults. There also is evidence of an increase in various autoantibodies (e.g., rheu­matoid factor) as a person ages, increasing the risk for autoimmune disorders. Older adults are more susceptible to urinary tract infections, respiratory tract infections, wound infections, and nosocomial infections. The mor­tality rate from influenza and bronchopneumonia is in­creased for the older adult population. Local organ factors and coincident diseases probably play a bigger role in the acquisition of these infections than age-related changes in immunity.³¹

Early detection of infections is more difficult in older adults because the typical symptoms, such as fever and elevated white blood cell count, often are absent.³² A change in mental status or decline in function often is the only presenting sign. It has been reported that frank delir­ium occurs in 50% of older adults with infections. Thus, infections in elderly persons may be far advanced at the time of diagnosis.