Defining and treating urinary infections.

Urinary infections increase not only with age but also with progressive disability and dependence. The reasons are not clear, but the rising incidence may be due to loss of bactericidal prostatic secretion in men; an increase in residual urine with ischemia of the bladder wall in both sexes; and recumbency, poor nutrition, and perhaps decreased defficiency of the autoimmune system in elderly patients with chronic diseases. Laboratory diagnosis of infections depends on the demonstration of 100,000 or more organisms of a single type in the urine. Fewer than this, or the presence of two or more types of organisms, indicates contamination. Careful collection and handling of urine specimens are necessary to avoid false-positive results. Pyelonephritis and acute cystitis are symptomatic infections and require antibiotic treatment. Chronic bacteriuria, however, usually does not produce symptoms, and since there is no clear evidence that it causes changes in renal function, antibiotic therapy usually is unnecessary.