If it spreads up to the bladder it is called cystitis. If the infection continues to spread it can reach the kidneys and is called pyelonephritis. UTI's can also be caused by the sexually transmitted diseases of Chlamydia and Mycoplasma. Any time the urinary tract isn't running smooth and clear the chances of an infection increase. Catheters are a common source of infections.
Extra care needs to be taken that they are clean and sterile.
People with diabetes may have a higher risk. Any disease that lowers the immune system can increase the risk of UTI's. Young men and boys seldom get infections. Women on the other hand see their chances increase as they get older. The exact reasons women are more susceptible aren't clear.