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Kidney infection (pyelonephritis)

Key points

  • Pyelonephritis is an infection of one or both of your kidneys.
  • Women get more kidney infections than men.
  • Symptoms of a kidney infection include feeling generally unwell, pain in your lower back, abdomen (tummy) or side, and a fever.
  • Your GP will usually prescribe antibiotics if you have a kidney infection.

Pyelonephritis is an infection of one or both of your kidneys. Anyone can get a kidney infection but it's most common in women and people who have an abnormal kidney

About kidney infection

You have two kidneys, which 'clean' your blood by filtering out water and waste products to make urine. Urine is stored in your bladder and then passed out of your body through your urethra. This is the tube that carries urine from your bladder and out of your body.

Illustration showing the position of the kidneys and surrounding structures

Pyelonephritis is a bacterial infection of your kidneys. The infection can be either acute or chronic. Acute and chronic refer to how long the condition lasts, rather than how severe it is. This factsheet will focus on acute kidney infection, which tends to come on quickly but should go within a couple of weeks.

Symptoms of kidney infection

The symptoms of an acute kidney infection often develop quickly over a few hours or a day and may include:

  • pain in your lower back, abdomen (tummy) or side (it may be only on one side)
  • a fever
  • shivering and chills
  • feeling weak
  • feeling sick or vomiting
  • diarrhoea

If you have any of these symptoms, contact your GP.

Around one in three women who get an acute kidney infection have symptoms of a bladder infection as well. This is also called cystitis, or a lower urinary tract infection (UTI). See our frequently asked questions for more information about UTIs.

Complications of kidney infection

An acute kidney infection can sometimes cause complications including:

  • a pocket of pus (abscess) in your kidney – this is called a pyonephrosis
  • your kidneys not working properly
  • blood poisoning (septicaemia) – this can happen if the bacteria that have caused your kidney infection get into your blood

You're more likely to develop complications if you:

  • are pregnant
  • have type 1 or type 2 diabetes
  • are over 65
  • have a persistent kidney infection
  • have kidney disease
  • have a urinary catheter fitted (a tube that takes urine from your bladder out of your body)
  • have a weakened immune system – for example, if you have HIV/AIDS (which reduces your ability to fight infection)

Causes of kidney infection

A kidney infection is usually caused by bacteria such as Escherichia coli (E. coli), which live in your bowel. The bacteria can get into your urinary tract if they spread from your anus to your urethra. The bacteria can enter your urethra and travel up into your bladder and will usually cause a lower UTI or cystitis. The bacteria can then travel up one or both of the tubes that connect your bladder to your kidneys (ureters) and cause a kidney infection.

You can also spread the bacteria when you have sex, as bacteria can enter your urethra. Bacteria and viruses can also be carried in your blood from other parts of your body to your kidney.

Women get more kidney infections than men. This is partly because the urethra is much shorter in women than in men. There is less distance for the bacteria to travel to the bladder.

You're also more likely to develop a kidney infection if you:

  • have an abnormal kidney
  • have a blocked ureter or kidney, for example by a kidney stone or an enlarged prostate gland
  • are pregnant (see our frequently asked questions for more information)
  • have diabetes
  • have a weakened immune system, for example, if you have HIV/AIDS
  • have had a UTI in the past year
  • have urinary incontinence

Diagnosis of kidney infection

Your GP will ask about your symptoms and examine you. He or she may also ask you about your medical history. Your GP will ask you to provide a urine sample. He or she will usually do a 'dipstick' test to confirm if you have a urinary infection. Your GP may send your urine sample to a laboratory to find out which type of bacteria is causing the infection.

In you have a severe kidney infection, your GP may recommend you go into hospital for further tests and treatment. Other tests may include:

  • a blood sample to see if you have signs of an infection
  • scans (such as a CT scan) to check for any problems or obstructions in your ureters or kidneys

Treatment of kidney infection


It’s important to drink enough fluids to prevent yourself from getting dehydrated. Make sure you get plenty of rest too.


If you need pain relief, you can take over-the-counter painkillers such as paracetamol. Always read the patient information leaflet that comes with your medicine and if you have any questions, ask your pharmacist for advice.

Your GP will usually prescribe antibiotics if he or she suspects that you have a kidney infection. It’s important to take the full course of antibiotics, even if your symptoms clear up before you finish them. Your symptoms should start to improve within a day or so. But if they get worse or you don't feel any better within 48 hours of starting treatment, contact your GP.

Hospital treatment

You may need hospital treatment if you’re:

  • pregnant
  • unable to keep down fluids or medicines
  • dehydrated
  • not responding to antibiotic treatment
  • diagnosed with blood poisoning (septicaemia)
  • at risk of developing complications

In hospital, you may have a drip inserted into a vein in your hand or arm to give you fluids and antibiotics.


You may need to have surgery if tests show that you have an obstruction (such as a kidney stone) in your ureters or kidneys.

Kidney infection and pregnancy

If you have a kidney infection when you're pregnant, it may lead to complications, such as:

  • kidney damage or even failure
  • having a baby with a low birth weight
  • premature labour
  • blood poisoning

If your GP suspects you have a kidney infection, he or she may send you for tests and treatment in hospital.

Prevention of kidney infection

If you often get a kidney infection or a UTI, your GP may advise you to take a low dose of antibiotics every day. How long you need to take them for will depend on your personal circumstances.

You can also develop a kidney infection from cystitis. If you get cystitis, try self-help measures or get prompt treatment to cure the condition. This will reduce the risk of the infection spreading to your kidneys.

Reviewed by Rachael Mayfield-Blake, Bupa Health Information Team, March 2014.

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  • This information was published by Bupa's Health Information Team and is based on reputable sources of medical evidence. It has been reviewed by appropriate medical or clinical professionals. Photos are only for illustrative purposes and do not reflect every presentation of a condition. The content is intended only for general information and does not replace the need for personal advice from a qualified health professional. For more details on how we produce our content and its sources, visit the about our health information page.

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