Trimethoprim resistance of Escherichia coli in outpatients in Finland after ten years' use of plain trimethoprim.

Development of trimethoprim resistance among Escherichia coli collected from urine samples in three areas in Finland was studied in 1978-1984. Three different trends of development of resistance were found: in the Turku area resistance has increased evenly during 1978-1982 from 5.4% to 10.1%, but thereafter a plateau seems to have been reached; in the Helsinki area resistance increased rapidly from 2.9% in 1980 to 11.1% in 1984, possibly due to the spread of a trimethoprim resistance transposon Tn7, which occurred significantly more often among E. coli strains in this area than in the Turku area; in the Rovaniemi area resistance has been at a plateau level, between 3.1 and 5.7%, during the whole study. No clear correlation between the consumption of trimethoprim and the level of resistance was found. The frequency of trimethoprim resistance in E. coli isolated from patients less than 65 years was 5.2% and in those isolated from patients greater than or equal to 65 years 14.7%.