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Bladder Infection (Cystitis)

Medically reviewed by Last updated on Aug 31, 2022.

What is Bladder Infection (Cystitis)?

Harvard Health Publishing

A bladder infection, also called cystitis, is caused by an abnormal growth of bacteria inside the bladder, the balloon-like organ that stores urine. Bladder infections are one of the most common bacterial infections to affect humans, with up to one-third of all females having at least one infection at some point in their lives.

Bladder Infection (Cystitis)

Bladder infections are classified as either simple or complicated. Simple bladder infections affect only healthy women with normal urinary systems. Bladder infections are rare in men who are otherwise healthy, so men are included in the complicated category with members of both sexes who have abnormal urinary systems.

  • Simple bladder infections — Simple bladder infections develop when bacteria migrate into the bladder. Because of the structure of the female urinary system, women are far more likely than men to get these infections. In women, the opening to the urethra (where urine comes out) is close to the rectum. Therefore, bacteria can migrate from the rectum, where bacterial counts are high, to the area around the vagina and urethra. From there, it is a short trip (4 centimeters, or less than 2 inches) through the urethra to the bladder. Sexual intercourse can propel these bacteria into the bladder, so there is an increased risk of bladder infections in sexually active women. Wiping toilet tissue from back to front after having a bowel movement also can transfer bacteria from the rectum to the urethra. For this reason, women should always try to wipe front to back.
  • Complicated bladder infections — Bladder infections are classified as complicated when they affect people with an abnormal urinary system that makes these infections more difficult to treat. All bladder infections are considered complicated when they affect men, because the long male urethra should prevent bacteria from getting into the bladder. However, if the normal flow of urine is obstructed or urine is retained in the bladder, bacteria will multiply there, increasing the risk of infection. One reason urine may be retained in the bladder is nerve damage, either from an injury, such as a spinal cord injury, or because of a disease, such as diabetes. The most common reason for obstruction of urine flow in men is an enlarged prostate, common in men older than 50. Patients with indwelling urinary catheters (a tube inserted into the urethra to drain urine) also have high rates of bladder infections because the bacteria climb along the wall of the catheter to the bladder.


Simple Bladder Infection
A bladder infection causes inflammation (irritation and swelling) of the bladder and urethra. This causes the sudden development of a predictable group of symptoms. Many women who have had a bladder infection in the past can identify the symptoms easily when they develop another infection. These symptoms usually include one or more of the following:

  • The need to urinate more often than normal, although only small amounts of urine are passed each time
  • A sudden need to urinate
  • Pain, burning or other discomfort during urination
  • The need to urinate at night
  • Pain in the lower abdomen
  • Blood in the urine
  • Urine that is cloudy, has an unpleasant odor or smells unusually strong

A bladder infection in a young child may cause new episodes of bedwetting as the only symptom.

Complicated Bladder Infection
People with complicated bladder infections usually have symptoms similar to those with simple infections. However, patients may also develop additional symptoms such as fever, chills, nausea, vomiting, flank pain, back pain, or confusion if the bacteria spread from the urinary system to the blood stream or kidney.

Complicated bladder infections require longer treatment than simple infections. Further testing may also be needed to look at the structure or function of the urinary system.


Your doctor will ask you about symptoms that are typical for bladder infection, and also ask you if you have fevers, chills, nausea, vomiting, flank pain or other symptoms that may suggest a more serious infection. If you have had bladder infections before, your doctor may be able to diagnose the problem over the phone if you are not pregnant and do not have any vaginal discharge. If the symptoms are not exactly like those of prior bladder infections, you probably will need an office visit and possibly a urine analysis.

Women with first-time bladder infections, all men, children and people with any potentially complicated bladder infection will need to visit a doctor. Your doctor will examine you and request a urine sample. He or she will do a urine analysis in the office to look for signs of active infection. The urine sample also may be sent to a laboratory for culture to identify the exact type of bacteria. Usually special testing, called sensitivity testing, also is done to determine which antibiotics will effectively fight the infection. Before you provide a urine sample, you should clean your urethral opening with a sterile wipe. This sample must be collected midstream during urination to avoid contaminating the urine with bacteria that live around the urethra.

Expected Duration

Women with simple bladder infections often improve within hours of taking the first dose of antibiotic, and all symptoms should go away within three days. However, people with complicated infections, such as men with enlarged prostate glands, may have prolonged symptoms. If patients have indwelling catheters in place, it is difficult to clear the urinary system of bacteria unless the catheter is removed.


Women may help to prevent bladder infections by wiping from front to back with toilet tissue and urinating after having sexual intercourse. Some women who have two or more bladder infections every year take an antibiotic after sexual encounters, three times per week, or daily to prevent infection. Other measures that may help to prevent bladder infections include going to the bathroom as soon as you feel the urge to urinate and drinking plenty of fluids every day. Some women who use a diaphragm for contraception have less frequent bladder infections by changing to a different method to prevent pregnancy. Some studies suggest that drinking cranberry juice may decrease your risk of acquiring a urinary tract infection.


Treatment varies, depending on the type of problem:

Simple Bladder Infection
Simple bladder infections in women usually are treated with one of three antibiotics: nitrofurantoin (Macrobid) twice per day for 5 days, trimethoprim sulfamethoxazole (Bactrim, Septra, Co-trimoxazole) or fosfomycin (Monurol) as a single oral dose. Women with recurring bladder infections (more than two per year) may benefit from preventive antibiotics, either taken as a regular dose or after sexual intercourse.

Complicated Bladder Infection
Complicated bladder infections are more difficult to treat. The choice of antibiotic, the strength of the medication and the length of treatment vary depending on the circumstances. Often, antibiotics need to be taken for 7 to 10 days. Patients with severe symptoms (fever, confusion, nausea, vomiting, etc.) that suggest the bacteria have spread to the kidney or blood usually will need to be treated in a hospital.

Treatment options

The following list of medications are in some way related to or used in the treatment of this condition.

View more treatment options

When To Call A Professional

Call your doctor's office if you feel pain or discomfort when you urinate, if you need to urinate more often than usual, or if you notice that your urine smells bad or contains blood. Women in their first trimester of pregnancy will have their urine checked for bacterial growth as part of their prenatal care, even if they have no symptoms of bladder infection.

If you have risk factors for developing complicated bladder infections (such as indwelling catheters or underlying abnormalities of the urinary system), you should be particularly careful to watch for these signs of infection. You also should seek immediate medical attention if you develop fever, chills, confusion, nausea, vomiting, or flank pain, which may suggest that a bladder infection has spread to the kidney or blood.


Treatment with antibiotics usually cures simple bladder infections. In some cases, an untreated bladder infection may spread upward in the urinary tract to affect the kidneys, causing pyelonephritis, which is inflammation and infection of the kidney. For complicated bladder infections, the outlook depends on the clinical situation. Patients may become severely ill if the infection spreads from the urinary system to the blood, a condition called urosepsis. Intravenous antibiotics are usually effective. Usually patients diagnosed with urosepsis need a longer course of antibiotics, but this can be accomplished at home with antibiotics taken by mouth.

Additional Info

National Kidney and Urologic Diseases Information Clearinghouse


Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.