Antimicrobial usage and microbial resistance in a university hospital during a seven-year period.

The prevalence of antimicrobial resistance among Staphylococcus epidermidis, Staph. aureus and Escherichia coli isolated in a university hospital, and the usage of antimicrobial agents within and outside the hospital was established for a seven-year period. The overall resistance to antimicrobial agents increased markedly for Staph. epidermidis but remained constant for the two other species. In Staph. epidermidis, a pronounced increase was seen in prevalence of resistance to penicillin, sulphonamides, trimethoprim, erythromycin and chloramphenicol, whereas resistance to streptomycin and tetracycline decreased. The trends in usage of beta-lactam antibiotics were identical within and outside hospital as opposed to the use of erythromycin and sulphonamides. The highest degree of correlation between antimicrobial usage and resistance to an antimicrobial was obtained using a corrected figure for antimicrobial usage paying regard not only to the use of a particular antimicrobial agent but also to a fraction of the usage of other antimicrobials which may co-select for the resistance trait.