A kidney infection (pyelonephritis) is a painful and unpleasant illness caused by bacteria travelling from your bladder into one or both of your kidneys.
It's more serious than cystitis, a common infection of the bladder that makes urinating painful.
If treated promptly, a kidney infection doesn't cause serious harm, but will make you feel very unwell. If a kidney infection isn't treated, it can get worse and cause permanent kidney damage.
Symptoms of a kidney infection often come on 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
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 and treated with antibiotics through an intravenous drip.
After taking antibiotics, 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 carries urine out of the body) and travels up through the bladder and into 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 include drinking plenty of fluids, keeping your genitals clean and treating any constipation.
Read more about preventing a kidney infection.