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.
You should see your doctor 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.
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.
Kidney infections are relatively rare.
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.
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 symptoms of a kidney infection usually develop quite quickly over a few hours or days. common symptoms include:
Children with a kidney infection may also have additional symptoms such as:
Contact your doctor if you have a high temperature, persistent pain, or if you notice a change to your usual pattern of urination. Contact your doctor immediately if you think your child may have a kidney infection.
If you have blood in your urine, you should always see your doctor so that the cause can be investigated.
Kidney infections require prompt treatment with antibiotics to help relieve symptoms and prevent complications developing.
Your doctor can carry out some simple tests to help diagnose a kidney infection.
See diagnosing kidney infections for more information.
A kidney infection happens when bacteria enters and infects one or both of your kidneys. The bacteria are usually a type called E. coli, which live in your bowel.
The bacteria get in through the opening of the urethra and move upwards through your urinary tract, first infecting your bladder and then your kidneys.
It's thought that one way the bacteria get into your urinary tract is by accidentally spreading from your anus to your urethra. This can happen if you wipe your bottom after going to the toilet and the soiled toilet paper comes into contact with your genitals. It can also happen during sex.
In rare cases, a kidney infection can develop if bacteria or fungi infect the skin and the infection spreads through your bloodstream and into your kidney. However, this type of infection usually only occurs in people with weakened immune systems.
Women and children are most at risk of developing a kidney infection, as well as other urinary tract infections (UTIs) such as cystitis.
In women, the urethra is closer to the anus than it is in men, making it easier for bacteria from the anus to enter the urethra accidentally. The female urethra is also much shorter than the male urethra (which runs through the penis). This makes it easier for bacteria to reach the bladder and move into the kidneys.
Other factors can also put you more at risk of developing a kidney infection, including:
To work out if you have a kidney infection, your doctor will ask you about your symptoms and your recent medical history.
They will usually also assess your general health by taking your temperature and measuring your blood pressure.
A urine test can help to establish whether you have a urinary tract infection (UTI). The test involves taking a small sample of urine and checking it to see if there are any bacteria in it.
However, a urine test can't tell whether the infection – if you have one – is in your kidneys or another part of your urinary system, such as your bladder.
For your doctor to be confident that you have a kidney infection, you need to have a positive urine test plus certain distinctive symptoms, such as a fever or a pain in your side.
You may be referred to a hospital for further testing if:
In these circumstances, scans can check your urinary tract for signs of problems. These include:
Read more about treating a kidney infection.
Most people with a kidney infection can be treated at home with a course of antibiotics, and possibly painkillers too.
If you're being treated at home, you will usually be prescribed a course of antibiotic tablets or capsules that lasts between seven and 14 days.
For most people – apart from pregnant women – antibiotics called ciprofloxacin or Co-amoxiclav Common side effects of ciprofloxacin include feeling sick and diarrhoea.
Co-amoxiclav can make the contraceptive pill and contraceptive patches less effective, so you may need to use another form of contraception during the course of treatment.
A 14-day course of an antibiotic called cefalexin is recommended for pregnant women.
Usually, you will start to feel better quite soon after treatment starts and you should feel completely better after about two weeks.
If your symptoms show no sign of improvement 24 hours after treatment starts, contact your doctor for advice.
Taking a painkiller such as paracetamol should help relieve symptoms of pain and a high temperature.
However, non-steroidal anti-imflammatories (NSAIDs) such as ibuprofen are not usually recommended to relieve pain during a kidney infection. This is because they may increase the risk of further kidney problems.
If you have a kidney infection, try not to "hover" over the toilet seat when you go to the loo, because it can result in your bladder not being fully emptied.
It's also important to drink plenty of fluids, because this will help prevent dehydration and will help to flush out the bacteria from your kidneys. Aim to drink enough so that you're frequently passing pale coloured urine.
Make sure that you get plenty of rest. A kidney infection can be physically draining, even if you're normally healthy and strong. It may take up to two weeks before you're fit enough to return to work.
In some instances, you'll need to be treated in hospital rather than at home. Hospital treatment may be needed if:
Most children with a kidney infection will be treated in hospital.
If you're admitted to hospital with a kidney infection, you'll probably be attached to a drip so you can be given fluids to help keep you hydrated. Antibiotics can also be given through the drip.
You'll have regular blood and urine tests to monitor your health and how effectively the antibiotics are fighting off the infection.
Most people respond well to treatment. As long as there are no complications, they're usually well enough to leave hospital within three to seven days. Treatment will usually switch to tablets or capsules after you stop receiving antibiotics through a drip.
The best way to prevent a kidney infection is to keep your bladder and urethra free from bacteria.
These self-help tips explain how you can do this.
Drinking plenty of liquids, particularly water, will help to wash bacteria from your bladder and urinary tract.
Drinking cranberry juice or taking cranberry extracts may also help prevent urinary tract infections (UTIs). But you should steer clear of cranberry juice or extracts if you're taking warfarin, a medicine used to prevent blood clots. Cranberry juice can make the effects of warfarin more potent, so there's a risk of excessive bleeding.
To help keep your urinary tract free from bacteria:
Constipation can increase your chances of developing a urinary tract infection (UTI), so try to treat any constipation promptly.
Recommended treatments for constipation include:
See your doctor if your symptoms don't improve after 14 days (or seven days for children with constipation).
Read more about treating constipation.
If you keep getting urinary tract infections (more than three a year is considered high), avoid using spermicide-coated condoms or diaphragms. This is because spermicide can stimulate the production of bacteria.
Stick to lubricated condoms without spermicide, because unlubricated ones can irritate the urethra and make it more vulnerable to infection.
Most kidney infections are treated successfully without any complications, although some people may develop further problems.
Complications of a kidney infection are rare, but you're more likely to develop them if you:
Some of the main complications of kidney infections are outlined below.
A kidney abscess is a rare but serious complication of a kidney infection. It's when pus develops inside the tissue of the kidney.
You're thought to be most at risk of developing a kidney abscess if you have diabetes.
The symptoms of a kidney abscess are similar to those of a kidney infection. The most common are:
Kidney abscesses are potentially serious because the bacteria inside the abscess can spread to other parts of your body, such as your bloodstream or lungs, and can be fatal.
Smaller abscesses can usually be treated with antibiotics through a drip. Surgery is usually required for larger abscesses. This involves draining the pus out of the abscess using a needle that's inserted into the kidney.
Blood poisoning (also called sepsis) is another rare, but potentially fatal, complication of kidney infection. It happens when bacteria spreads from the kidneys into the bloodstream. Once bacteria are in your blood, the infection can spread to any part of your body, including all of the major organs.
In someone with a kidney infection, the symptoms of blood poisoning include:
Blood poisoning is a medical emergency that usually requires admission to a hospital intensive care unit (ICU) while antibiotics are used to fight the infection.
If you're taking certain medications for diabetes, such as metformin or angiotensin-converting enzyme (ACE) inhibitors, they may have to be temporarily withdrawn until you recover. This is because they can cause kidney damage during an episode of blood poisoning.
Another rare but potentially fatal complication of a kidney infection is a condition called emphysematous pyelonephritis (EPN).
EPN is a severe infection where the tissues of the kidneys are rapidly destroyed and the bacteria causing the infection begin to release a toxic gas, which builds up inside the kidneys.
The exact cause of EPN is unclear, but almost all cases are in people with diabetes.
The usual treatment is emergency surgery to remove some, or all, of the affected kidney. It's possible to live a full and active life with only one kidney.
In very rare cases, a kidney infection can cause severe kidney damage that results in kidney failure. This is when the kidneys stop working properly.
A kidney infection can also cause other complications, including high blood pressure(hypertension) or [premature labour and birth].
Important: Our website provides useful information but is not a substitute for medical advice. You should always seek the advice of your doctor when making decisions about your health.