Objective: To determine whether asymptomatic bacteriuria (ABU) prior to Bacillus Calmette-Guérin (BCG) immunotherapy has an impact on the oncological results and overall tolerability of BCG treatment in patients with non-muscle-invasive bladder cancer (NMIBC).

Materials and methods: We analyzed retrospectively all patients who received ≥ 1 BCG instillations as treatment of NMIBC in Helsinki University Hospital and Turku University Hospital during 2009–2018. Patients submitted urine specimen 1–7 days prior to the initiation of BCG therapy. ABU was classified as having any positive urine culture but no dysuria or fever. Our primary endpoints were 5-yr recurrence-free survival and progression-free survival. Discontinuation rate of BCG therapy was a secondary endpoint.

Results: We identified 795 patients, of whom 154 (19%) had ABU prior to the first BCG instillation. The 5-yr recurrence-free survival rates in the uninfected and bacteriuric groups were 63% (95% confidence interval [CI]: 59–67%) vs. 69% (95% CI: 62–78%), respectively (hazard ratio [HR] 0.83, 95% CI 0.60–1.14). The 5-yr progression-free survival rates were 88% (95% CI: 86–90%) vs. 89% (95% CI: 84–94%), respectively (HR 0.86, 95% CI 0.50–1.49). The 3-yr discontinuation-free survival rates were 51% (95% CI: 47–54%) vs. 51% (95% CI: 44–60%), respectively (HR 0.98, 95% CI 0.75–1.28).

Conclusion: ABU did not significantly affect BCG immunotherapy outcomes. Intravesical BCG during ABU is safe, with similar discontinuation rates, indicating very similar treatment tolerability.