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Bladder infection (cystitis)

Medically reviewed by Last updated on Oct 19, 2023.

What is a 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 healthy men and non-pregnant women with normal urinary systems. Bladder infections occur much more commonly in women compared to men.

Symptoms of a bladder infection

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:

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.

Diagnosing a bladder infection

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, pregnant women, 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.

Treatment options

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

View more treatment options

Expected duration of a bladder infection

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.

Preventing a bladder infection

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.

Treating a bladder 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.

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 Institute of Diabetes and Digestive and Kidney Diseases

Further information

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