Introduction 

A kidney infection is a painful and unpleasant illness that usually happens when bacteria travel up from your bladder into one or both of your kidneys.

The medical name for a kidney infection is pyelonephritis. It's more serious and different from cystitis, which is a common infection of the bladder that makes urinating painful.

If treated promptly, a kidney infection doesn't cause serious harm but it will make you feel very unwell. If a kidney infection isn't treated, it can get worse and cause permanent kidney damage.

Often the symptoms of a kidney infection come on quickly within a few hours. You can feel feverish, shivery, sick and have a pain in your back or side.

Read more about the symptoms of a kidney infection.

When to see your GP

You should see your GP if you have a fever and persistent tummy, lower back or genital pain, or if you notice a change to your usual pattern of urination.

Most kidney infections need prompt treatment with antibiotics to stop the infection from damaging the kidneys or spreading to the bloodstream. You may also need painkillers.

If you're especially vulnerable to the effects of an infection, for example if you have a pre-existing health condition or are pregnant, you may be admitted to hospital as a precaution and be treated with antibiotics through an intravenous drip.

Antibiotic treatment is usually a very effective way of treating a kidney infection and you should feel completely better after about two weeks.

In rare cases, a kidney infection can cause further problems. These include blood poisoning (sepsis) and a build-up of pus in the kidney called an abscess.

Read more about treating a kidney infection and the complications of a kidney infection.

What causes a kidney infection?

A kidney infection usually happens when bacteria – often a type called E. coli – gets into the urethra (the tube which urine passes through) from the anus and travels up through the bladder into one or both of the kidneys.

Read more about the causes of a kidney infection.

Who's at risk?

Kidney infections are relatively rare. It's estimated that one in every 830 people develops a kidney infection each year in the UK.

They can happen at any age, but are much more common in women. In fact, women are six times more likely to get a kidney infection than men. This is because a woman's urethra is shorter, making it easier for bacteria to reach the kidneys.

Younger women are most at risk because they tend to be more sexually active, and having frequent sex increases the chances of getting a kidney infection.

Younger children are also vulnerable to developing kidney infections because they may be born with an abnormality of the urinary tract or have a condition called vesico-ureteric reflux, where there is a backflow of urine from the bladder up to the kidneys.

Can kidney infections be prevented?

You can reduce your chances of developing a kidney infection by keeping your bladder and urethra free from bacteria. This can be achieved with simple measures such as drinking plenty of fluids and practicing good genital hygiene.

Read more about preventing a kidney infection.

The urinary tract

The urinary tract is made up of the:

  • kidneys, which extract waste materials from the blood and convert it into urine
  • ureters, the tubes that run from the kidney to the bladder
  • bladder, the organ that stores urine
  • urethra, the tube that carries urine out of the body

The kidneys 

The kidneys are two bean-shaped organs roughly four inches in length. They are found towards the back of the abdomen on either side of the spine.

They remove waste products from the blood. The clean blood is then transferred back into the body and the waste products are passed out of the body as urine.

An infection that develops inside the urinary tract is known as a urinary tract infection (UTI). As the parts of the urinary tract are all connected, a UTI that develops in one section can spread to another.

What do our kidneys do?

The kidneys filter waste products from the blood before turning it to urine. This video explains in detail how the kidneys function.

Media last reviewed: 15/11/2013

Next review due: 15/11/2015

Page last reviewed: 11/12/2012

Next review due: 11/12/2014