Bladder Infection (Cystitis)


What Is It?

A bladder infection, also called cystitis, is caused by the abnormal growth of bacteria inside the urinary bladder. Bladder infection is the most common bacterial infection to affect humans, with up to one-third of all females having at least one infection at some point in their lives.

In general, 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 susceptible to these infections than men. 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 abnormality of the 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 gaining access to the bladder. However, if there is any obstruction of the normal urinary flow or retention of urine in the bladder, bacteria will multiply there, increasing the risk of infection. If there is any neurological abnormality of the bladder, either from traumatic nerve damage (such as a spinal cord injury) or diseases that cause nerve damage (such as diabetes), then it will be harder to empty the bladder and urine may be retained. 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, often passing only small amounts of urine (frequency)
  • A sudden need to urinate (urgency)
  • Pain, burning or other discomfort during urination (dysuria)
  • The need to urinate at night (nocturia)
  • Pain in the lower abdomen
  • Blood in the urine (hematuria)
  • Urine that is cloudy, has an unpleasant odor or has an unusually strong smell

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

Complicated bladder infection
People with complicated bladder infections usually have symptoms similar to those with simple infections. The difference is that the infection often requires a treatment with antibiotics for a longer time. Also, complicated bladder infections have a greater risk of spreading to the kidney and the bloodstream. Symptoms of kidney infection include nausea, vomiting, fever, chills and back or flank pain.


Your doctor will ask you about symptoms that are typical for bladder infection (frequent urination, sudden need to urinate, burning with urination, blood in urine, etc.), 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 can 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/or 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 may be sent to a laboratory for culture to determine the exact type of bacteria and special testing called sensitivity to determine which antibiotics will work well to 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 resolve 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.


Women can help to prevent bladder infections by wiping from front to back with toilet tissue after a bowel movement and by urinating after having sexual intercourse. Some women with frequent bladder infections (more than two 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 the urge to urinate arises, drinking plenty of fluids every day, and avoiding feminine-hygiene products that might irritate the urethral opening. Some women find that taking showers rather than baths decreases the number of bladder infections.


Treatment varies, depending on the clinical situation:

Asymptomatic bacteruria
Many people have bacteria in their urine, but they have no symptoms of infection. This condition, called asymptomatic bacteriuria, needs to be treated only if the woman is pregnant, or has a chronic kidney condition (such as a kidney transplant) that might get worse if the bacterial growth is not eliminated. Pregnant women with asymptomatic bacteruria usually are treated with antibiotics to decrease the risk of kidney infection and preterm labor.

Simple bladder infection
Simple bladder infections in women usually are treated with a three-day course of an antibiotic, such as trimethoprim sulfamethoxazole (Bactrim, Septra, Co-trimoxazole). Women with recurrent bladder infections (more than two per year) may benefit from preventive antibiotics, either taken as a daily dose or after sexual intercourse.

Complicated bladder infection
Complicated bladder infections are more difficult to treat. The choice of antibiotic and the strength and duration of treatment vary depending on the circumstances. Often, antibiotics need to be taken for 10 days or more.

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.


Treatment with antibiotics usually cures simple bladder infections. In rare 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 prognosis depends on the clinical situation. Antibiotics are usually effective, but they may need to be taken for long periods, and the risk of recurrence can be high.

Johns Hopkins patient information

Last revised:

Diseases and Conditions Center

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All ArmMed Media material is provided for information only and is neither advice nor a substitute for proper medical care. Consult a qualified healthcare professional who understands your particular history for individual concerns.