Symptoms & Causes of Kidney Infection (Pyelonephritis)

What are the symptoms of kidney infections?

Symptoms of kidney infections vary by age. Symptoms may include

  • chills
  • fever
  • pain in your back, side, or groin
  • nausea
  • vomiting
  • cloudy, dark, bloody, or foul-smelling urine
  • frequent, painful urination
A woman lying in bed, checking her temperature with a thermometer.
Symptoms of a kidney infection may include chills; fever; and frequent, painful urination.

A child younger than 2 years old with a kidney infection may only have a high fever.

An adult older than age 65 with a kidney infection may have none of the typical symptoms. An older person may only have problems with thinking, such as

  • confusion
  • hallucinations
  • jumbled speech

Seek care right away

Seek care right away if you have kidney infection symptoms. A kidney infection can sometimes lead to a dangerous condition called sepsis, which can be life threatening. Symptoms of sepsis include fever, chills, rapid breathing and heart rate, rash, and confusion.

A kidney infection that becomes chronic, or long lasting, can cause permanent damage to your kidneys.

What causes a kidney infection?

Kidney infections are caused by bacteria or viruses.

Scientists believe that most kidney infections start as a bladder infection that moves upstream to infect one or both of your kidneys. Most often, the infection is caused by bacteria that normally live in your bowel. The urinary tract has several ways to prevent infection from moving up the urinary tract. For example, urination most often flushes out bacteria before it reaches the bladder. Sometimes your body can’t fight the bacteria and the bacteria cause a UTI. If you don’t get medical treatment to stop the infection, the bacteria may infect your kidneys.

In some cases, your blood can carry bacteria or viruses from another part of your body to your kidneys.

April 2017
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This content is provided as a service of the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), part of the National Institutes of Health. The NIDDK translates and disseminates research findings through its clearinghouses and education programs to increase knowledge and understanding about health and disease among patients, health professionals, and the public. Content produced by the NIDDK is carefully reviewed by NIDDK scientists and other experts.

The NIDDK would like to thank:
Ann E. Stapleton, MD, FIDSA, FACP, University of Washington School of Medicine