What Is It?

Pyelonephritis is a kidney infection usually caused by bacteria that have traveled to the kidney from an infection in the bladder.

Women have more bladder infections (also called urinary tract infections) than men because the distance to the bladder from skin, where bacteria normally live, is quite short and direct. Usually, however, the infection remains in the bladder.

A woman is more likely to develop pyelonephritis when she is pregnant. Pyelonephritis and other forms of urinary tract infection increase the risk of premature delivery.

A man is more likely to develop the problem if his prostate is enlarged, a common condition after age 50. Both men and women are more likely to develop pyelonephritis if they have any of the following conditions:

  • An untreated urinary tract infection
  • Diabetes
  • Nerve problems that affect the bladder
  • Kidney stones
  • A bladder tumor
  • Abnormal backflow of urine from the bladder to the kidneys, called vesicoureteral reflux
  • An obstruction related to an abnormal development of the urinary tract

Tests or procedures that involve the insertion of an instrument into the bladder also increase the risk of urinary tract infections and pyelonephritis.

Children sometimes develop pyelonephritis because of an abnormality in the bladder that allows urine there to flow backwards (reflux) into the ureter, the connection between the kidney and bladder. This can lead to scarring of the kidney.

Rarely, pyelonephritis is so severe that it is life threatening, especially in older people or in those with an impaired immune system.


Pyelonephritis usually begins with a sudden, intense pain in one flank, the area just beneath the lower ribs in the back. This pain can travel around the side toward the lower abdomen, or down to the groin. There also can be a high fever, shaking chills, and nausea and vomiting. The urine may be cloudy, tinged with blood, or unusually “strong” or foul-smelling. Additional bladder-related symptoms can include the need to urinate more often than normal, and pain or discomfort during urination.


If your doctor is concerned that you have a kidney infection, he or she will ask you about other medical problems, any past infections and your recent symptoms. He or she also will check your vital signs (temperature, heart rate, blood pressure), and will press on your abdomen and flanks to see if there is tenderness near the kidney. In women, the symptoms of pyelonephritis may be similar to those of certain sexually transmitted diseases, so your doctor may recommend that you have a pelvic examination.

To diagnose pyelonephritis, your doctor will test your urine, and often your blood, for evidence of infection. Samples of your blood and urine will be tested in a laboratory, to see if they contain bacteria. People with pyelonephritis may have bacteria in both their blood and their urine, especially if they have high fevers. It usually takes about 24 to 48 hours to identify the type of bacteria, and determine which antibiotics will be most effective.

Expected Duration

Most patients with uncomplicated cases of pyelonephritis find that their symptoms improve after one to two days of treatment with antibiotics. However, even after symptoms improve, antibiotics must be taken for 10 to 14 days.


To help prevent pyelonephritis if you have had a previous episode or are at risk:

  • Drink several glasses of water each day. Water discourages the growth of infection-causing bacteria by flushing out your urinary tract. This flushing also helps to prevent kidney stones, which can increase the risk of pyelonephritis.

  • Drink cranberry juice or take vitamin C supplements. Both cranberry juice and vitamin C may deter the growth of bacteria by making your urine more acidic.

  • If you are a woman, wipe from front to back. To prevent the spread of intestinal and skin bacteria from the rectum to the urinary tract, women should always wipe toilet tissue from front to the back after having a bowel movement or urinating.

  • Decrease the spread of bacteria during sex. If possible, women should clean the area around the genitals before having sex. Women also should urinate after sexual intercourse to flush bacteria from the bladder. Some women who have frequent urinary tract infections after sexual activity can take antibiotics around the time of intercourse to prevent an infection.

If there is a structural problem with the urinary system, such as blockage from a stone, or a developmental abnormality, a variety of surgical procedures can be done to restore normal urinary function and prevent future episodes of pyelonephritis.


Doctors treat pyelonephritis with antibiotics. In most uncomplicated cases of pyelonephritis, the antibiotic can be given orally (by mouth), and treatment usually lasts for at least two weeks. Commonly used oral antibiotics include trimethoprim with sulfamethoxazole (Bactrim and others), ciprofloxacin (Cipro) or levofloxacin (Levaquin), but the choice of antibiotic will depend on your history of allergies and laboratory testing of the bacteria causing the infection. Once you finish the full course of antibiotics, your doctor may ask for another urine sample to check that bacteria are gone.

If you have high fever, shaking chills or severe nausea and vomiting, you are more likely to become dehydrated and may be unable to take oral antibiotics. In that case, you may require hospital treatment so that antibiotics can be given intravenously (into a vein). High fever and shaking chills also may be signs that your kidney infection has spread to your bloodstream and can travel to others parts of your body. If your doctor is concerned that you may have an obstruction (such as a kidney stone that is stuck in the ureter) or a structural abnormality in your urinary system, other tests may be ordered, such as a computed tomography (CT) scan, ultrasound, intravenous pyelogram (which shows an outline of the urinary tract on X-rays) or cystoscopy, an inspection of the inside of the bladder using a thin, hollow, tubelike instrument.

When To Call A Professional

Call your doctor immediately if you have symptoms of pyelonephritis (particularly fever and flank pain, with or without urinary symptoms), especially if you are pregnant.


A single episode of uncomplicated pyelonephritis rarely causes permanent kidney damage in an otherwise healthy adult. However, repeated episodes of pyelonephritis can cause chronic (long-lasting) kidney disease in children, people with diabetes, and adults who have structural abnormalities of the urinary tract, or nerve diseases that disrupt bladder function. Pyelonephritis can become chronic if an infection cannot be cleared readily, as in a person with a kidney stone or other developmental abnormality of the urinary system.

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.