Background: Controversy exists on whether urinary tract infection (UTI) is a risk factor for urinary bladder cancer (UBC). Here, the association is investigated using data from one of the largest bladder cancer case–control studies worldwide. Methods: Information on (i) history and age at onset of regular cystitis (‘regular low-UTI') and (ii) number and age at onset of UTI treated with antibiotics (‘UTI-ab') from 1809 UBC patients and 4370 controls was analysed. Odds ratios (ORs) and 95% confidence intervals (CI) adjusted for age, education, smoking, and use of aspirin/ibuprofen were generated, for men and women separately. Results: Regular low-UTI was associated with an increased UBC risk (men: OR (95% CI) 6.6 (4.2–11); women: 2.7 (2.0–3.5)), with stronger effects in muscle-invasive UBC. Statistically significant decreased risks (ORs ～0.65) were observed for up to five UTI-ab, specifically in those who (had) smoked and experienced UTI-ab at a younger age. In women, UTI experienced after menopause was associated with a higher UBC risk, irrespective of the number of episodes. Conclusions: Regular cystitis is positively associated with UBC risk. In contrast, a limited number of episodes of UTI treated with antibiotics is associated with decreased UBC risk, but not in never-smokers and postmenopausal women.
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