Kidney infection 


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.

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 - a ‘balloon-shaped’ organ that is used to store urine
  • urethra - the tube that runs from the bladder through the penis (in males) or vulva (in females) through which urine is passed

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

See the Health A-Z topics about UTIs in children and UTIs in adults for more information.

A kidney infection is an uncommon type of infection. If the infection is treated, it is not usually serious, but it can make a person feel very unwell. The medical term for a kidney infection is pyelonephritis.

Symptoms of a kidney infection include:

  • a high temperature (fever) of 38ºC (100.4ºF) or above
  • pain in the side of your abdomen
  • being sick

See kidney infection - symptoms for more information.

The kidneys

The kidneys are two bean-shaped organs that are located on either side of the body, just underneath the ribcage. They are part of the urinary tract (see box, left). The main role of the kidneys is to filter out waste products from the blood before converting it into urine.

A kidney infection usually occurs when bacteria (usually E. coli bacteria) passes from the urethra into one of the kidneys. The urethra is the tube that runs from the bladder through the penis in men and the vulva in women. Urine is passed through the urethra.

In most cases of kidney infection, only one kidney is usually affected.

How common are kidney infections?

Kidney infections are an uncommon type of infection. It is estimated that 1 in every 830 people will develop a kidney infection in any given year.

Women are six times more likely to get a kidney infection than men. This is due to a number of factors, such as a woman’s urethra being shorter than a man’s, which makes it easier for bacteria to reach the kidneys.

Younger women are most at risk of developing a kidney infection. This is because they tend to be sexually active and frequent sexual intercourse is a risk factor for kidney infections. See kidney infection - causes for more information.

Kidney infections are also slightly more common during pregnancy, affecting 1 in 50 pregnant women.

Younger children are also more vulnerable to developing kidney infections because their small urinary tract makes it easier for bacteria to reach their kidneys. It is estimated that 1 in 20 cases of high temperature in children is a result of a kidney infection.

Types of kidney infection

There are two main types of kidney infection. They are:

  • uncomplicated kidney infection - where the infection occurs in an otherwise healthy individual
    complicated kidney infection - where underlying factors (see below) make a person more vulnerable to developing an infection, more likely to experience complications and less likely to respond to conventional treatment

Examples of underlying factors that increase a person’s chances of developing a kidney infection  include:

See kidney infection - causes for more information.


For cases of uncomplicated kidney infection, the outlook is excellent. Most people respond well to treatment with oral antibiotics (tablets or capsules) and make a full recovery.

For cases of complicated kidney infection, the outlook is usually good. However, people with the condition may be admitted to hospital as a precaution and be treated with intravenous antibiotics (antibiotics that are injected into a vein).

Complications of kidney infections are uncommon, but they are potentially very serious and include blood poisoning (sepsis) and kidney failure. See kidney infection - complications for more information.

  • show glossary terms
Kidneys are a pair of bean-shaped organs located at the back of the abdomen. They remove waste and extra fluid from the blood, and pass them out of the body as urine.
The bladder is a small organ near the pelvis that holds urine until it is ready to be passed from the body.
Bacteria are tiny, single-celled organisms that live in the body. Some can cause illness and disease, and some are good for you.

Last reviewed: 11/04/2011

Next review due: 11/04/2013


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suze_87 said on 20 December 2010

in october i had a UTI symptoms such as burning pain when going to the loo and i went to the doctors have a urinaylsis done and comfirmed a UIT. I was given 4 days worth of antibiotics which wasnt doing anything. By the 5th day i woke up in the night with colic pain in my right back. it felt like my kidney squeezing and cramping up so painful and i couldnt walk. in the morning i went back to the doctors who said i may have a kidney stone and gave me some pain killers. over the weekend the pain got worse and i was being sick even when only drinking water i was sick. so i went to the doctors then A&E for an IVU and there were no stones. the SHO said i have either passed them and they also gave me a kidney infection. after being on more antibiotics the GP requested a urine sample which i sent off and came back that the infection was resistant to the original antibiotics. so i was prescribed Augmentin and 6 weeks or more later i still have blood in my urine and sometimes my right back aches but not as bad as before and i also feel that my bladder has weaken due to the infection. It was a horrible experience

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suzielindsay09 said on 29 August 2010

Since having kidney stones when I was a child I have faced infections all through life but now I seem to have a sore bladder if pressed in or when laughing to hard. I know when I have an infection as I get a pain in my lower back which I have also been getting. Should I be worries about the sore bladder and take further action..?

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beckys said on 26 January 2010

I am still waiting for my last lot of lipotripsy, I spent 2 weeks in hospital nearly four years ago when one was stuck in my bladder tube and also had stents put in, I had three stones and even now I am still getting infections and waiting for my final lot of treatment but since having them I seem to get run down more easily and the first thing that happens is my kidney starts to ache, I am hoping after this last session that I will feel better!

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amos9000 said on 23 January 2010

the kidneys create a hormone that tells your bones to make red blood cells, if they have been infected then it may not have done this and you might have become a bit anemic which might be why you are feeling week. as for the thickened arms and legs im not certian it could be that your kidneys are having trouble getting rid of excess fluid causing it to build up.
I had a kidney infection years ago and thought i was fine so i left it. untill about 2 months ago i felt completly fine then started getting tired and week with swelling in my legs and was found to have end stage kidney failure. So i would get it checked out just to be sure theres nothing goin on,.

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PAULA L said on 21 January 2010

i was found to have kidney stones last april, after many months of continually complaining to my doctor. i was at last sent for a ct scan where it was found i had 3 largish ones in my left and a huge one stuck in my ureter. it had been there for some time and had caused blockage and infection of the kidney. after stents being placed in both and lithotripsy on the smaller ones , spending a few days in hospital on 3 occasions with intravenous anti-biotics, various x-rays and blood tests , we at last think the worst is over. my question is , why do i still feel so unwell. i'm always tired and i'm so weak i still cant carry on in my usual capacity. i also have thickened arms and legs , not puffy or swollen but larger than usual and slightly numb; ,and the pain !!!!!!!! has anyone else had these problems as nothing has been properly explained to me ?

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