UTIs are more common in women because their urethra is shorter and the exit is closer to the anus. Sexual intercourse is the most usual cause of infection, and in many cases a UTI can result after a woman's initial sexual encounter. Men are somewhat protected because their urethra is longer and the prostate gland can actually block bacteria. However, as the sexes age, the incidence of infection is similar in both sexes. Patients who are on a urinary catheter are at risk for UTI.