['BK polyomavirus (BKV) infection remains a significant cause of nephropathy and graft loss. Fluoroquinolones inhibit BKV replication in vitro, and small studies suggest in vivo benefit. A strategy of fluoroquinolone prophylaxis directed specifically against BKV has not been formally tested against a control group in kidney transplant recipients.', 'We retrospectively compared the impact of a change in antibiotic prophylaxis practice from no BKV prophylaxis (Group 1, n=106, July-December 2009) to BKV prophylaxis with ciprofloxacin 250 mg twice daily for 30 days (Group 2, n=130, January-June 2010) on the rate of BKV infection during the first 12 months after kidney transplantation.', 'Baseline demographics, transplant characteristics, induction immunosuppression, and 1-year incidence of acute rejection were similar between groups. Group 1 had fewer patients on maintenance corticosteroids (65.1% vs. 83.2%, P=0.002). At 3 months, Group 1 had a significantly higher risk of developing BK viremia (0.161 vs. 0.065, P=0.0378) and viruria (0.303 vs. 0.146, P=0.0067) compared with Group 2, but this difference disappeared at 12 months for both viremia (0.297 vs. 0.261, P=0.6061) and viruria (0.437 vs. 0.389, P=0.5363). Adjusting for the difference in steroid use did not change the results. There was a trend toward higher incidence of biopsy-proven BKV nephropathy in Group 1 (4.7% vs. 0.8%, P=0.057).'] Does ciprofloxacin prophylaxis in kidney transplant recipients reduce BK virus infection at 3 months but not at 1 year?