Kidney Infection (Pyelonephritis)

Symptoms or signs may include:

• Chills and high fever
• Frequent, painful urination
• Back, side (under the ribs), and groin pain
• Nausea and vomiting

Very young children (younger than two years old) may only have a high fever. They may not feel pain or have problems passing urine. Older people, also, may not show typical signs. Instead, they may show signs of confusion, muddled speech or hallucinations.

This infection can be life threatening. It is important to seek medical care quickly if you think you have a kidney infection.

Although the urinary system is designed to keep bacteria out, problems can occur. Bacteria found in the intestines can enter the urinary tract through the urethra. These bacteria can travel up into the bladder. When this happens it can cause cystitis (inflammation of the bladder). If the infection continues up to the kidneys, it can cause kidney infection. This problem is rare but it can be severe. About 1 in every 30 cases of cystitis leads to a kidney infection.

You are more likely to get a kidney infection if you have frequent bladder infections or have a structural problem in the urinary tract. Urine normally flows only in one direction—from the kidneys to the bladder. If the flow of urine is blocked or flows in the wrong direction, infections can happen. Urine flow can be blocked by many things, including:

• kidney stones,
• tumors inside or outside the urinary tract and
• structural problems of the urinary tract.

People with diabetes or a weak immune system are at high risk for infections. Pregnant women with UTIs should be seen by their health care provider and treated as soon as possible. A kidney infection in a pregnant woman can be very serious.

Many problems in the pelvis and abdomen can cause symptoms that look like kidney infection. Your health care team will want to diagnose your problem correctly to learn what’s happening and find the best treatment.

To diagnose the problem, your health care team may use the following tests:

• A medical history. You will be asked questions about your symptoms, when they began and about your general health history.
• Physical exam. You will receive a general medical exam to collect blood and urine samples. The health care team will likely press your abdomen to check for pain or tenderness.
• Urinalysis. A sample of your urine will be tested to look for signs of infection. High counts of white blood cells and bacteria mean that there is an infection.
• Urine culture. In a urine culture, bacteria in urine may grow on a culture dish within a few days. This information will help the health care team determine the best antibiotic to use.
• Blood cultures. A blood culture can tell if your infection has spread to your blood.
• Computed tomography (CT scan). A CT scan is not necessary to diagnose kidney infection, but it shows detailed 3D images of the urinary tract and kidneys to detect problems. A CT would also see if there is a blockage that needs treatment.
• Kidney ultrasound. Ultrasound can create images of the kidneys and ureters to show if there are wounds, stones or other things that block the urinary tract. This information can help guide treatment decisions.

Your health care team will also look for problems that can cause kidney infection, such as kidney stones or birth defects. These things can be treated to prevent future infections. Your treatment will be based on a clear diagnosis of the problem.

Kidney infections are usually treated with antibiotics. If the infection is very bad, then you may need to go to a hospital to get antibiotics in your vein (IV). To heal the infection and stop it from coming back, it is common to get two or more weeks of antibiotics.

Surgery may be needed if a block in the urinary tract or a birth defect is found.

Generally, you will feel much better within a few days of treatment for the infection. Even though the symptoms may be gone, it is of great value to finish the entire course of medicine so it doesn’t return.

What if I don’t treat kidney infection?

Untreated infection can damage the kidneys and lead to long term problems. In rare cases, kidney infections can lead to kidney disease, high blood pressure, or kidney failure. If kidney infection spreads to the bloodstream it can cause a serious problem called sepsis.

Can the bacteria that cause kidney infections be resistant to antibiotics?

Yes, the bacteria can be resistant to some, but it not all antibiotics. Both urine and blood cultures are taken before starting medicine. These tests help the health care team know which medicine would work best for your case.

What can I do to avoid this problem?

Women should wipe from the front to the back after having a bowel movement. This cleaning will help move bacteria away from the urethra opening. Peeing after sex may help to flush out bacteria in the urethra. Some forms of contraception may help (not including diaphragms or spermicidal foam).

What if I am pregnant?

Urinary tract infections (UTI) during pregnancy are dangerous for both mother and baby. These infections should be treated quickly. There are safe medicines to use during pregnancy to cure the infection.

Updated December 2024.