Transferable trimethoprim resistance in three Finnish hospitals.

Resistance to trimethoprim in urinary tract isolates was studied in the Turku City Hospital in 1979 and 1980-81 and in the Turku and Kuopio University Central Hospitals in 1980-81. In the Turku City Hospital no changes occurred during this time in the frequency of strains highly-resistant to trimethoprim (MIC greater than 1000 mg/l) or of those in which transferable resistance was demonstrated. However, the nature of resistance has changed since 1979, when the only transferable pattern was trimethoprim-ampicillin resistance. In 1980-81 over half of the transfer-positive stains transferred only trimethoprim resistance. In the university hospitals the strains highly-resistant to trimethoprim occurred in 36.8% of strains resistant to greater than or equal to 8 mg/l. This is significantly less than 68.7% observed at the same time in the Turku City Hospital. Among the highly-resistant strains the frequency of those transferring resistance was the same in the university hospitals as in the Turku City Hospital.