Positive correlation between the age of patients and the degree of antimicrobial resistance among urinary strains of Escherichia coli.

We have studied the resistance of urinary strains of Escherichia coli in relation to patients' age. A total of 4146 samples of urine was collected during 1984-1990 from patients staying in an acute care university hospital and in a long-term care city hospital in Finland. In the city hospital, the proportion of strains resistant to either ampicillin, trimethoprim, sulphonamides, or to all of these simultaneously (multi-resistant), correlated with increase in age of the patients. In the university hospital, a clear increase was observed in trimethoprim-resistant and multiresistant isolates. Such correlation with age was not observed among catheterised patients in either hospital. Whether this is due to cumulative lifetime use of antimicrobials remains to be studied. We conclude that the incidence of resistant strains of E. coli correlates with patients' age among both chronic and acute care patients who are not catheterised. This is important in the choice of empirical treatment for urinary tract infections of elderly people.