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OBJECTIVES: To investigate the cumulative incidence proportion of disseminated or local Bacillus Calmette-Guérin (BCG) infections after adjuvant BCG instillations in patients with non-muscle-invasive bladder cancer (NMIBC).

PATIENTS AND METHODS: We analysed the timing and occurrence of BCG infections and absolute and relative risk in relation to patient characteristics available in the Swedish nationwide database 'BladderBaSe 2.0'. The cumulative incidence proportion of a BCG infection was indicated by a reported diagnosis of tuberculosis (TB) in the patient registry or filing a prescription for tuberculostatic drugs.

RESULTS: The cumulative incidence proportion was 1.1% at the 5-year follow-up in 5033 patients exposed to adjuvant BCG instillations. The incidence rate was highest during the first 2 years after start of BCG instillations. Women had a lower risk than men (hazard ratio 0.23, 95% confidence interval 0.07-0.74). Age and calendar time at diagnosis, comorbidity, tumour risk group, previous medication with corticosteroids, immunosuppressive drugs, or time between transurethral resection of the bladder tumour and commencing the adjuvant BCG instillation were not associated with risk.

CONCLUSIONS: These data further supports that the overall risk of a BCG infection after BCG-instillation treatment for NMIBC is low. The great majority of infections occur in the first 2 years, calling for an awareness of the diverse symptoms of BCG infection during this period. We provide evidence for male sex as a risk factor; however, the statistical precision is low and with a risk of selection bias, making it difficult to rule out the other suggested risk factors without further studies with different approaches.