The two main types of bladder infections are:

• Community-acquired bladder infections. These infections occur when people who aren't in a medical care facility, such as a hospital or nursing home, develop a bladder infection. This condition is common in women between the ages of 30 and 50, but is rare in men of the same age. However, men older than 50 may be at risk of this type of infection because of prostate enlargement, a common condition that can block urine flow in older men.

• Hospital-acquired, or nosocomial, bladder infections. These infections occur in people in a medical care facility, such as a hospital or nursing home. Most often they occur in those who have had a urinary catheter placed through the urethra and into the bladder to collect urine, a common practice done before some surgical procedures, for some diagnostic tests, or as a means of urinary drainage for elderly people or people confined to bed. Nosocomial bladder infections can occur when a temporary or permanent catheter is placed in the bladder of a person who is unable to void spontaneously.

UTIs typically occur when bacteria enter the urinary tract from the outside, usually through the urethra, and begin to multiply. The urinary system is designed to keep out such microscopic invaders. The bladder secretes a protective coating that prevents bacteria from attaching to its wall. Urine also has antibacterial properties that inhibit the growth of bacteria. However, certain factors increase the chances that bacteria will take hold and multiply into a full-blown infection.

Sometimes cystitis is referred to as honeymoon cystitis, because this bladder infection commonly occurs in women as a result of sexual intercourse. During sexual activity, bacteria may be introduced into the bladder through the urethra. But even sexually inactive girls and women are susceptible to lower urinary tract infections because the anus, a constant source of bacteria, is so close to the female urethra.