In addition to being a woman, risk factors have been identified on the basis of age, sexual activity and medical history:

Recurrence Half of all women experience a UTI, and 1 in 10 have three or more a year
Sex Bacteria can enter the urethra during intercourse
Contraception Diaphragms and some spermicidal agents may increase the risk
Pediatrics Recurrent UTIs associated with pyelonephritis, vesicoureteral reflux and asymptomatic bacteriuria
Menopause Reduced estrogen changes the urinary tract and makes it more vulnerable
Blockages Kidney stones (or an enlarged prostate) or any other urinary tract blockage can prevent the bladder from flushing out harmful bacteria
Medical Conditions Diabetes and other conditions that may slow or stop the body from fighting infection increases risk
Catheter Use/SCI Using catheters to urinate – for instance, when hospitalized, paralyzed or dealing with neurological problems – may lead to UTIs