Kidney Infection (Pyelonephritis)


What is kidney infection (pyelonephritis)?

Infection in the urinary tract can involve the lower tract especially the bladder (cystitis), prostate (prostatitis) or the upper tract and kidney (pyelonephritis). It is usually a bacterial infection. The disease occurs in roughly three to seven of every 10,000 people in the United States. The occurrence in pregnant women is about 2 percent. It is readily treatable if diagnosed early.

A bacteria called Escherichia Coli (E Coli) causes about 90 percent of kidney infections. The bacteria migrate from the genitals through the urethra (the tube that removes urine from the body) into the bladder and up the tubes (ureters) that connect the bladder to the kidneys.

Some bacteria, such as staphylococcus infections, can enter the kidneys from the bloodstream.

Symptoms and Causes

What are the causes of kidney infections (pyelonephritis)?

Normally, bacteria are flushed out by the flow of urine. However, several problems can increase the risk of a kidney infection. These problems can include:

  • Structural abnormalities (strictures, stents, stones, surgery) blocking urine flow.
  • An enlarged prostate gland (benign prostatic hyperplasia) compressing the urethra.
  • Backflow (reflux) of urine from the bladder to the kidneys.
  • If your immune system is affected (low white blood cell count, use of certain medications, HIV, cancer, an organ transplant).
  • Pregnancy, during which time the enlarging uterus can squeeze the ureters and reduce the flow of urine, allowing the bacteria to migrate to the kidneys.
  • Uncontrolled diabetes mellitus.

What are the symptoms of kidney infection?

A number of symptoms can indicate to your doctor that you may have a kidney infection. The more severe the symptoms, the more likely the infection involves the kidney. Symptoms of a kidney infection include:

  • Sudden onset of chills
  • Fever over 100 degrees Fahrenheit
  • Pain in the groin, lower back or side
  • Nausea
  • Vomiting
  • Abdominal muscle spasm

More general symptoms of upper kidney infection include:

  • Flushed or reddened skin
  • Painful urination
  • Increased urination
  • Unproductive attempts to urinate despite feelings of urgency
  • General ill feelings
  • Cloudy urine
  • Abnormally colored urine
  • Blood in the urine
  • Foul smelling urine

If you experience any of these sudden onset symptoms, please seek medical attention.

Diagnosis and Tests

How are kidney infections (pyelonephritis) diagnosed?

Two common laboratory tests are performed to diagnose kidney infections (pyelonephritis). A urine sample is examined under a microscope to determine if white and/or red blood cells are present. The urine is also sent to the lab to see if bacteria grow in a urine culture. If a person is very sick, blood cultures may also be sent. The strain of bacteria that are cultured will determine the type of therapy used in your treatment.

Pyelonephritis can often be treated without X-ray studies, unless your doctor suspects there may be an addition problem. CT scans produce images of structures and organs and these scans are usually done without contrast (dye). A renal ultrasound may sometimes suffice for evaluation.

Management and Treatment

How are kidney infections (pyelonephritis) treated?

A physician will treat the disease based on his or her examination. He or she may start the patient on the standard treatment of a course of antibiotics before the lab tests results are available. The medication may change once the exact strain of bacteria is revealed by the lab tests.

If the treatment is effective, the patient should feel better in two to three days. If not, your healthcare provider will start looking for additional problems. Most antibiotic treatments last for 14 days and it is essential that patients take the pills as recommended for the full 14 days even though symptoms may disappear after a few days. The disappearance of symptoms does not mean all bacteria are killed. Some may remain and the infection may reappear.

There is also a concern that those bacteria that remain may develop resistance to the medication. For some reason the disease is more difficult to treat in men and they may have to take medication for up to six weeks. Patients with severe illness, those that have significant nausea and vomiting, high fevers, significant pain and signs of dehydration may be hospitalized for a few days while the antibiotics are administered intravenously. Urine samples are taken after about six weeks of treatment and examined to insure the bacterial infection is eradicated.


Can kidney infections (pyelonephritis) be prevented?

Kidney infections can be prevented by keeping bacteria out of the urinary tract and bladder. Infections in the kidney often start as a lower tract infection in the bladder. By preventing these infections, you may be able to prevent kidney infections.

There are several ways to avoid infection and keep your kidneys healthy. These tips can include:

  • Hydration: It is important to drink adequate fluid (not only water) every day but there is no specific recommendation that applies to every patient.. The amount can change if you have certain medical conditions or live in a particularly hot climate. Talk to your healthcare provider about the recommended amount of water you need each day.
  • Urinate completely: When you need to urinate, empty your bladder completely. Holding in your urine can be harmful and can promote the growth of bacteria. Urinating every several hours can help to flush any bacteria out of your body, protecting it from an infection.
  • Urinate after having sex: Urinating after sex helps to remove any bacteria that may have gotten into the body. Men and women should both do this to prevent infections.
  • Practice good hygiene: Keeping yourself clean can help protect your body from infections. After a bowel movement, wipe from front to back to push bacteria away from the urethra (an opening in the body). This is especially important for women.

Outlook / Prognosis

What is the outlook for kidney infections (pyelonephritis)?

With treatment, the outlook for kidney infections (pyelonephritis) is very positive. It is vital that you take all of any prescribed medications for the infection. You may begin feeling better shortly after beginning a treatment, but still need to take the entire prescribed treatment.

Last reviewed by a Cleveland Clinic medical professional on 05/22/2019.


  • National Kidney Foundation. Urinary Tract Infections ( Accessed 5/23/19.
  • National Institute of Diabetes, Digestive and Kidney Diseases (NIDDK). Pyelonephritis: Kidney Infection ( Accessed 5/23/19.

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