Experimental pyelonephritis. XV. Increased susceptibility to E. coli infection in old rats.

One of the most interesting features of the epidemiology of urinary tract infections is an increasing prevalence with advancing age.`' Infections are exceedingly uncommon in men below age 50 and the rates in elderly women are two to three times the rates in women below age 40. There are a number of possible explanations for this pattern. Urinary infections might confer a survival advantage on those infected; persons without infections would then have higher death rates and the result would be increasing rates of positive urine cultures with advancing age. This possibility is unlikely since all the clinical features with which urinary infections have been correlated would tend to decrease survival. The course of infections in the elderly may be more prolonged. Thus, at any given time there would be more infections in older women. This too, is not likely to be the explanation for the increased rates in old age since, despite some disagreement, analyses of various features (including response to treatment) does not indicate significant differences between old and young women.1' It is possible that treatment of urinary infections has been improving over the years. If this were so, older subjects who developed their infections 20 or 30 years ago might have had less chance to be treated effectively at the onset, whereas, young persons developing infections for the first time might be more likely to receive effective therapy. This, too, would result in higher rates of urinary infection in older women. Unfortunately, there is little evidence that even today the long-term effect of antibiotic treatment is very satisfactory, and there are some data to suggest that antibiotic treatment may not influence the outcome of infection four years later.' The most likely explanation for the increased rates of urinary infections in older persons is that there is an increasing susceptibility to urinary tract infections with advancing age. Increased susceptibility up to now has been considered a result of the increasing rates of lower urinary tract abnormali-