Investigation of host defense mechanisms in the aged as determinants of nosocomial colonization and pneumonia

Host defense mechanisms of hospitalized patients older than 60 yr of age were compared to those of younger hospitalized patients and to nonhospitalized controls to determine if altered defense mechanisms could be correlated with the nosocomial carriage of pathogens and the development of hospital-acquired pneumonia. The following age-associated alterations were noted: changes in lymphocyte responses to mitogens, decreased concentrations of IgG and IgM, depressed polymorphonuclear leukocyte function, and altered concentrations of complement components in hospitalized patients. Serum opsonins for Escherichia coli were normal. There was an age-associated increase in the prevalence of the pharyngeal carriage of both Staphylococcus aureus and aerobic gram-negative bacilli. Hospital-acquired pneumonia developed in 2 of 12 patients over 75 yr of age and in 1 of 34 patients aged 60 to 75, a higher rate than reported for hospitalized patients nationally. A clear correlation between host defense alteration and the colonization or development of pneumonia was not identified.