Urinary culture sensitivity after a single empirical antibiotic dose for upper or febrile urinary tract infection: A prospective multicentre observational study.

Objectives: Urinary culture sensitivity after antibiotics administration is unknown. This study aimed to describe the diagnostic sensitivity of urine cultures from patients' first, second, and third micturition samples after a single dose of empirical antibiotics given for upper and/or febrile urinary tract infections, as well as searched for factors influencing diagnostic sensitivity over time.

Methods: We collected consecutive urine samples from adult patients with an upper or febrile urinary tract infection diagnosed at four secondary hospital emergency rooms. One sample was collected before a first dose of empirical antibiotic treatment and up to three samples were collected from consecutive postadministration micturition. The main outcome was the number of positive cultures growing uropathogens with ≥10 colony forming units (CFUs) for men and ≥10 for women. Identical analyses were performed for any identified CFU and ≥10 CFU cut-off points. Time between antibiotic administration and first negative urinary culture was noted, which could have been at the time of any of the three postantibiotic urine samples. We used a Cox regression analysis for age- and sex-adjusted analyses.

Results: A total of 86 of 87 patients' preantibiotic cultures (99%) were positive compared with 26 of 75 (35%; p < 0.001), 15 of 50 (30%; p < 0.001), and 1 of 15 (7%; p < 0.001) of the first, second, and third postantibiotic samples, respectively, and missing 14 of 21 (67%), 13 of 17 (76%), and 7 of 7 (100%) of uropathogens with antibiotic resistance, respectively. The times needed for 25%, 50%, and 75% of cultures to be negative were 1.5, 2.9, and 9 hours, respectively, after antibiotic administration. Older age, male sex, non-Escherichia coli pathogens, urinary tract disease, comorbidity burdens, and urinary catheters prolonged time to negative culture, but were not significantly associated after adjustment. Uropathogens were found at ≥10 CFU in 15 of 75 (20%), 7 of 50 (14%), and 0 of 15 (0%) of the three postantibiotic micturition samples, respectively, and in any identified CFU in 48 of 75 (64%), 23 of 50 (46%), and 1 of 15 (7%), respectively.

Conclusion: Urinary culture sensitivity decreases rapidly after administering antibiotics.