A kidney infection is a painful, unpleasant illness that usually happens when bacteria travel up from your bladder into one or both of your kidneys.
It's different from - and more serious than - cystitis, which is a common infection of the bladder that makes urinating painful.
Kidney infection, medically known as pyelonephritis, doesn't usually pose a serious threat to your health if treated promptly, but it can make you feel very unwell. And, if a kidney infection isn't treated, it can get worse and cause permanent kidney damage.
Often the symptoms come on quickly, within a few hours, and they can make you feel feverish, shivery, sick and with a pain in your back or side.
When to see your GP
You should see your GP quickly if you have symptoms of a kidney infection.
Most kidney infections need prompt treatment with antibiotics. That's to stop the infection from damaging the kidneys or spreading to the bloodstream. You may need painkillers too.
If you're especially vulnerable to the effects of an infection, for example if you have a pre-existing health condition or you're pregnant, you may be admitted to hospital as a precaution and treated with antibiotics that are given by intravenous drip into a vein.
Read more about treating a kidney infection.
What causes a kidney infection?
The kidneys are two bean-shaped organs on either side of the body, just underneath your ribcage. Their main role is to filter out waste products from blood. These waste products, along with excess fluid, are then converted into urine and passed out of the body.
A kidney infection usually happens when bacteria, often a type called E. coli, accidentally gets into the urethra (the tube through which urine passes out of the body) from the anus and then travels up through the bladder into one of the kidneys.
In most cases of kidney infection, only one kidney is affected.
Read more about the causes of a kidney infection.
Who's at risk?
Kidney infections aren't that common. It's estimated that 1 in every 830 people will develop a kidney infection in any given year.
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 than a man's, which makes it easier for bacteria to reach their kidneys.
Younger women are most at risk because they tend to be sexually active, and having frequent sex increases the chances of getting a kidney infection. Kidney infections are also slightly more common during pregnancy.
Younger children are also 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 actually a result of a kidney infection.
There are steps you can take to reduce your risk of kidney infection. Find out more about how to prevent kidney infection.
Symptoms of kidney infection
The symptoms of a kidney infection include:
Children with a kidney infection may also have additional symptoms such as:
When to seek medical advice
Contact your GP if you have a high temperature, persistent pain, or if you notice a change to your usual pattern of urination.
Kidney infections require prompt treatment with antibiotics to help relieve symptoms and prevent complications developing.
Now, find out how kidney infection is diagnosed.
Causes of kidney infection
A kidney infection happens when bacteria enters and infects one or both of your kidneys. The bacteria is 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 (see box, right).
It's thought that one way the bacteria get in to your urinary tract is by accidentally spreading from your anus to your urethra. This can happen if you wipe your bottom after going to 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.
Who's most likely to get a kidney infection?
Women 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 accidentally enter the urethra. 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 put you more at risk of developing a kidney infections. They are listed below.
Kidney infections in men
Kidney infections are much less common in men than in women, mainly because the male urethra is shorter and further from the anus than in women. Also, in men, the skin and tissue around the urethra is drier than in women, which means that bacteria do not breed as easily. And, the fluid that's produced by the prostate gland has an anti-bacterial effect.
However, some men do get kidney infections, particularly if they:
Now, find out how kidney infections are diagnosed.
Diagnosing kidney infection
To work out if you have a kidney infection, your GP will ask you about your symptoms and your recent medical history. They'll 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's any bacteria in it.
But 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 GP 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.
Further testing is usually only required if:
In these circumstances, two types of hospital scan can check your urinary tract for signs of problems. They are:
Read about how a kidney infection is treated.
Treating kidney infection
Once you've been diagnosed with a kidney infection, your GP will discuss your treatment with you.
Most people can be treated at home by taking a course of antibiotics and possibly painkillers too.
If you're being treated at home, you will be prescribed a seven-day course of antibiotic tablets or capsules.
Co-amoxiclav sometimes makes 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.
Contact your GP for advice if your symptoms fail to improve within 24 hours after starting to take antibiotics.
Taking a painkiller, such as paracetamol, should help to relieve symptoms of pain and a high temperature.
It's also important to drink plenty of fluids because this will help prevent you becoming dehydrated, and it will help to flush out the bacteria from your kidneys. Aim to drink enough so that you're frequently passing pale coloured urine.
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.
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.
Treatment at hospital
In some instances, you'll need to be treated in hospital rather than at home. Hospital treatment may be needed if:
If you're admitted to hospital with a kidney infection, you'll probably be attached to a drip so that 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 monitor 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.
Now, read about the complications of kidney infection.
Complications of kidney infection
There are three main complications of a kidney infection. They are:
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 intravenous antibiotics. Surgery is usually required for larger abscesses. It normally involves draining the pus out of the abscess using a needle that's inserted into the kidney.
Blood poisoning 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, which is medically known as sepsis, 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 that are causing the infection begin to release 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.
Preventing kidney infection
Most kidney infections develop following an infection of another part of your urinary tract, such as cystitis.
So, the best way to prevent a kidney infection is to keep your bladder and urethra free from bacteria. These self-help tips explain how to do this.
Drink plenty of liquids
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 to prevent urinary tract infections. But steer clear of cranberry juice or extracts if you're taking warfarin (a medicine that's used to prevent blood clots). Cranberry juice can make the effects of warfarin more potent, so there's a risk of the interaction between the two causing excessive bleeding.
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 GP if your symptoms don't improve after 14 days (or seven days for children with constipation).
Read more about how to treat constipation.
Be careful with contraceptives
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, making it more vulnerable to infection.
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