Kidney Infection- A Guide

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A kidney infection usually occurs when a bacterial infection (typically e-coli bacteria) moves up from the bladder or urethra and into one of the kidneys.

Symptoms of kidney infection
Causes of kidney infection
Diagnosing kidney infection
Treating kidney infection
Preventing kidney infection

See also: Kidney Health Products


The urethra is the tube that runs from the bladder through the penis or vulva. Urine is passed through the urethra.

The medical term for a kidney infection is pyelonephritis. Typical symptoms of a kidney infection can include:

  • a high temperature (fever) of 38ºC (100.4ºF) or above,
  • pain in the side of your abdomen,
  • vomiting, and
  • diarrhoea.

The kidneys

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

Usually, only one kidney is affected by an infection.

Are kidney infections common

Kidney infections are an uncommon type of infection. In England, it is estimated that 28 to 35 people out of every 100,000 will get a kidney infection in any given year.

Kidney infections are more common in:

  • women than in men,
  • pregnant women,
  • children who are under two,
  • people over 60.

Types of kidney infection

There are two main types of kidney infection:

  • Uncomplicated kidney infection: the person is in good health and the infection is unlikely to cause any serious complications.
  • Complicated kidney infection: the person affected is more vulnerable to the effects of infections. This could be due to a pre-existing health condition.


In cases of uncomplicated kidney infection, treatment with antibiotics quickly relieves symptoms, and most people will fully recover within two weeks.

In cases of complicated kidney infection, treatment usually requires injections of antibiotics (intravenous antibiotics), and the person may be admitted to hospital as a precaution.

There is a small risk of serious complications developing in complicated kidney infection, such as blood poisoning (sepsis) or a kidney abscess, which can occasionally be life threatening.

There is also the risk that the kidney could become damaged as a result of the infection and, in the most serious cases, the damage could cause the kidney to stop working altogether (kidney failure).

Despite the risk of complications, deaths from kidney infections are now very rare. This is mainly due to the introduction of antibiotics in the 1940s.

Symptoms of kidney infection

The symptoms of a kidney infection usually develop quickly over the space of a few hours or a day. Symptoms include:

  • a high temperature (fever) of 38ºC (100.4ºF) or above,
  • uncontrollable shivering,
  • nausea,
  • vomiting, and
  • diarrhoea.

You may also experience pain in your side, back or groin. The pain can range from moderate to severe, and it is often worse when you are urinating.

Additional symptoms can also be caused by a corresponding infection of the bladder (cystitis) and/or the urethra (urethritis). These symptoms include:

  • pain, or a burning sensation during urination (dysuria),
  • needing to urinate frequently or urgently,
  • feeling that you are unable to urinate fully,
  • cloudy, bloody or bad-smelling urine, and
  • pain in your lower abdomen.

Causes of kidney infection

Any infection that occurs within your urinary system, such as in the kidneys, is known as a urinary tract infection (UTI).

What is the urinary tract?

The urinary tract is made up of:

  • the kidneys,
  • the bladder,
  • the ureters (the tubes that carry urine from the kidneys to the bladder), and
  • the urethra (the tube that passes from the bladder to the penis or vulva, through which you urinate).

When food is digested, waste products are left behind in the blood. They are removed by either the kidneys or the liver.

The most important part of the waste products that are removed by the kidneys is known as urea. Urea is mixed with water to produce urine. The urine is passed down from the kidneys, through the ureters and into the bladder. Once the bladder is full of urine, it is passed from the body through the urethra when we urinate.

How does a kidney infection develop?

A kidney infection occurs when bacteria enters and infects one or both of your kidneys. Bacteria, typically E.coli living in your colon, are often the cause of kidney infections.

The bacteria enter through the opening of the urethra and multiply in the bladder. The bacteria then move upwards through the urinary tract, infecting your bladder and, eventually, your kidneys.

It is thought that the bacteria can be inadvertently spread from your anus to your urethra. This can happen if, when wiping your bottom after going to toilet, the toilet paper comes into contact with your genitals.

In rare cases, a kidney infection can also develop if bacteria or fungi infect the skin, and the infection is spread through your bloodstream into your kidney. This type of infection usually only occurs in people who have weakened immune systems.

Risk factors

Women are more likely to develop a kidney infection, as well as other urinary tract infections (UTIs) such as bladder infections (cystitis). This is because in women the urethra is located closer to the anus than it is in men, making it easier for bacteria from a woman’s anus to reach the urethra.

The female urethra is also much shorter than the male urethra (which runs through the penis), making it easier for bacteria to reach the bladder and then move into the kidneys.

Other risk factors for kidney infections are listed below.

  • Having a condition that obstructs or blocks your urinary tract, such as kidney stones.
  • Having a condition that prevents you from emptying your bladder fully.
  • Having a weakened immune system due to diabetes, for example, or chemotherapy.
  • Being female and sexually active. This is because sexual intercourse can irritate the urethra, enabling bacteria to travel more easily through it and into your bladder.
  • Being male and having an enlarged prostate gland.
  • Having a urinary catheter (a tube that is inserted into your bladder in order to drain away urine).

Diagnosing kidney infection

Before diagnosing a kidney infection, your GP will ask you about your symptoms and your recent medical history. They will also take your temperature and measure your blood pressure in order to assess your general state of health.

Urine test

A urine test can usually determine whether you have a urinary tract infection (UTI). During a urine test, a small sample of urine will be taken and checked for the presence of bacteria.

However, there is no single test to determine whether the infection is in your kidneys or in another part of your urinary system, such as your bladder. Despite this, there are certain distinctive symptoms, such as a fever or a pain in your side, which should enable a confident diagnosis of a kidney infection to be made.

Treating kidney infection

Once a kidney infection has been diagnosed, your GP will assess whether you can be treated at home or whether you should be admitted to hospital as a precaution.

You may be admitted to hospital if:

  • you are pregnant,
  • you are over 60 years of age,
  • you have symptoms of severe vomiting,
  • you have symptoms of severe pain,
  • you are dehydrated,
  • you are unable to pass urine, or the amount of urine you are passing is severely reduced,
  • you have a blockage in your kidneys, such as kidney stone,
  • you have diabetes,
  • you have been undergoing chemotherapy and/or radiotherapy,
  • you have a previous history of kidney disease,
  • you have had a previous history of recurring kidney infections,
  • you have HIV,
  • you have sickle-cell anaemia, or
  • you have cancer.

Treatment at home

If you can be treated for a kidney infection at home, you will be given a course of antibiotic tablets to take (oral antibiotics).

After taking the antibiotics for a few days, you should notice a significant improvement in your symptoms. However, it is important that you finish the course to ensure that your infection is completely cured.

Contact your GP if you do not notice any improvement in your symptoms after taking antibiotics for 48 hours.

The antibiotics that are used to treat a kidney infection can cause drowsiness, so while you are taking them you should avoid driving and operating complex or heavy machinery.

Make sure that you drink plenty of fluids because this will help to relieve your symptoms of fever, and will also help to prevent dehydration.

However, there are a number of health conditions, such as kidney disease, where you may be required to limit your fluid intake. Your GP can advise you about your daily fluid intake.

Paracetamol can be used to ease symptoms of pain.

Treatment at hospital

If you are admitted to hospital with a kidney infection, you will probably be attached to a drip so that you can be given fluids to help keep you hydrated. Antibiotics can also be administered through the drip.

You will be given regular blood and urine tests that carefully monitor your health and measure the antibiotics’ effectiveness in fighting off the infection.

Most people respond well to treatment, and leave hospital within three to seven days.

Complications of kidney infection

Kidney abscesses

In particularly severe cases of kidney infections, pockets of pus can build up within the tissue of the kidney. These pockets are known as abscesses.

Symptoms of kidney abscesses include:

  • weight loss,
  • blood in your urine, and
  • abdominal pain.

Surgery may be required in order to drain the pus out of your kidney.


Sepsis is the medical name for blood poisoning. It is a rare but potentially fatal complication of kidney infections. Sepsis occurs when the bacteria spreads from your kidneys to your bloodstream. Once bacteria are present in your blood, infection can then spread to any part of your body, including all the major organs.

Symptoms of sepsis include:

  • low blood pressure, which makes you feel dizzy when you stand up,
  • a change in mental behaviour, such as confusion or disorientation,
  • diarrhoea,
  • reduced urine flow,
  • cold and clammy skin,
  • pale skin, and
  • loss of consciousness.

Sepsis is a medical emergency, and it usually requires admission to an intensive care unit (ICU) so that the functions of the body can be supported while antibiotics are used to fight the infection.

Emphysematous pyelonephritis

Emphysematous pyelonephritis (EPN) is another rare but potentially fatal complication of a kidney infection.

EPN is a severe type of infection, where the kidney tissues are rapidly destroyed and the bacteria that are responsible for the infection begin to release toxic gas that builds up inside the kidneys.

Symptoms of EPN include:

  • a high temperature (fever) of 38ºC (100.4ºF) or above,
  • abdominal pain,
  • nausea,
  • vomiting, and
  • mental confusion.

The exact cause of EPN is unclear, but having poorly-controlled diabetes seems to be a major risk factor for the development of the condition.

Left untreated, EPN is fatal because the bacteria and toxic gas cause multiple organ failure. EPN requires emergency surgical treatment, and it is usually necessary to remove some or all of the affected kidney.

Preventing kidney infection

Most cases of kidney infections develop from a pre-existing infection of the urinary tract. Therefore, the best way to prevent a kidney infection is to keep your bladder and urethra free from bacteria. The advice below explains how this can be done.

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 help to prevent urinary tract infections. However, you should not consume cranberry juice or extracts if you are taking warfarin (a medicine used to prevent blood clots).

Treat constipation promptly

Constipation can increase your chances of developing a urinary tract infection (UTI). Recommended treatments include increasing the amount of fibre in your diet (20-30g of fibre a day), using a mild laxative on a short-term basis, and drinking plenty of fluids.

You should see your GP if your symptoms do not improve after 14 days. Children should see their GP if their symptoms have not improved after seven days.

Other useful advice

To help keep your bladder and urethra free from bacteria:

  • Go to the toilet as soon as you feel the need to urinate, rather than holding it in.
  • Wipe from front to back after going to the toilet.
  • Practise good hygiene by washing your genitals every day and before having sex.
  • Empty your bladder after having sex.