Increased rates of trimethoprim resistance in uncomplicated urinary tract infection: cause for concern?

AIMS: To assess changes in trimethoprim resistance over 2 years in bacteria causing uncomplicated urinary tract infections (UTIs) presenting to a representative group of general practitioners (GPs) in Christchurch.
METHODS: Seventy-six randomly selected GPs in Christchurch (the Christchurch Sentinel network) participated in the study. Using the same methodology as in the previously reported 2000 collection, midstream urine (MSU) samples were prospectively collected for standard microbiological analysis on all women between the ages of 16 and 50 years presenting with symptoms of dysuria and frequency and who had positive dipstick testing for either nitrites, leucocytes, or both. MSUs were submitted for bacterial colony counts and resistance testing of isolates present in numbers >105 cfu/ml of urine.
RESULTS: 216 dipstick positive specimens were collected in the survey period; 105 of these fulfilled criteria for significant bacteriuria. Trimethoprim resistance was found in 16 (15.2%) overall, with a resistance rate for Escherichia coli (E. coli) to trimethoprim of 17.7%. When compared to the proportions of organisms resistant in the 2000 study, there were apparent but non significant increases in the total resistance among pathogens (+6.7%) and E. coli resistance (+5.8%). Rates of antibiotic resistance of all organisms to nitrofurantoin (2.9%) and norfloxacin (0.95%) remain low. There was a statistically significant increase in resistance among all women presenting with symptoms and a positive dipstick test (+5.3%; 95% CI: 1.5%-9.1%). For a woman in this age group presenting with symptoms of urinary tract infection and a positive dipstick test, we estimate that her probability of having a trimethoprim-resistant organism in 2002 was 7.4% compared with 2.7% in 2000.
CONCLUSION: Trimethoprim resistance of E. coli causing uncomplicated UTI appears to be rising in Christchurch. This may reflect the promotion and extensive use of this agent as first-line treatment. Whilst these data indicate that trimethoprim remains a reasonable first-line empiric treatment in this condition, this may change if trimethoprim resistance continues to rise. The apparent increase over a relatively short period (2-3 years) demonstrates the importance of regular surveillance. A third study is required to confirm whether this is a significant trend.