Secular trends in rates and etiology of nosocomial urinary tract infections at a university hospital.

To examine changing trends in the microbial etiology of nosocomial urinary tract infections, we reviewed culture data from a surveillance database for the calendar years 1982 to 1991. The overall rates of nosocomial urinary tract infections have increased significantly during the last decade from 2.63 per 1,000 patient-days to 4.35 per 1,000 patient-days (p = 0.0023). For specific isolates the rates of yeasts, Klebsiella pneumoniae and group B streptococcus have increased significantly during the last decade. The rates of Escherichia coli, Proteus species and Pseudomonas species have all decreased. Analysis of these secular trends can provide important information relating to the etiology of nosocomial urinary tract infections. It is likely that antibiotic "pressure" has influenced the microbiology of infections and that altered case-mix would explain much of the increase in rates. However, the multiple reasons for these secular trends and their precise contributions to them are unknown.