[Infections in the elderly. Part I. Etiology and pathogenesis].

An increase in the percentage of elderly subjects in the society has been observed in Poland and in the world from many years. Ageing is associated with an impaired functioning of many organs and systems, including the immune system, respiratory system and the urinary tract. Although circulating immune cell numbers and immunoglobulin levels are relatively unchanged, changes in cell activity (especially T-lymphocyte function, among others an increase in CD4+/CD8+ ratio and increase in the proportion of memory cells with a concomitant decrease in naive T lymphocytes) cause a decline in both cell-mediated immunity and antibody response to immunogen. Age-associated changes in local defenses are also important: decreased functioning of respiratory system, ageing of the skin, atrophy of urinary tract, and decrease in gastric acidity. All of these impairments result in decreased resistance to infections. People over the age of 65 are at increased risk of developing pneumonia, influenza and urinary tract infections. It presents not only a serious clinical problem but also epidemiological and social one.