What causes urinary tract infections in the elderly?

It depends: In elderly men enlarged prostate, neurogenic bladder, urinary retention, indwelling Foley catheters, diabetes. In elderly women neurogenic bladder, vaginitis, diabetes.

Menopause, Prostate: Women stop producing estrogen after menopause. Lack of this hormone causes urethral lining + introitus (skin between labia) to thin out and reduce secretions of immunoglobulins from vagina. All reduce natural UTI defense mechanisms. Constipation and urinary incontinence are other factors. Prostate enlargement causing some retention of urine plus obstruction to flow increases chances of utis.