Kidney Infection in Adults
Pyelonephritis in Adults

A kidney infection can cause an unpleasant illness which is sometimes serious. Treatment includes antibiotics and painkillers. If the kidney was previously healthy then you are likely to make a full recovery. Complications occur in some cases such as kidney damage or blood infection (septicaemia).

What is this leaflet about?

This leaflet only deals with acute (sudden onset) kidney infection in adults. The medical term for an acute kidney infection is acute pyelonephritis. There are separate leaflets on related topics called 'Cystitis (bladder infection) in Women', 'Urine Infection When You are Pregnant', 'Urine Infection in Men', and 'Urine Infection in Children'. Also, this leaflet does not deal with chronic pyelonephritis (a condition where the kidney is scarred as a result of repeated infections).

Understanding the kidneys and urinary tract

There are two kidneys, one on each side of the abdomen. They make urine which drains down the ureters into the bladder. Urine is stored in the bladder and is passed out through the urethra from time to time when we go to the toilet.

What are the symptoms of a kidney infection?

Symptoms usually develop quickly, over a few hours or so, and may include:

• pain in a loin (side of the abdomen over the kidney).
• high temperature (fever).
• feeling sick (nausea).
• vomiting and/or diarrhoea.
• blood in the urine.
• you may also have symptoms of a bladder infection. For example, pain when you pass urine, and going to the toilet often.

Not all the symptoms may develop, and sometimes a kidney infection can just cause vague symptoms. For example, just feeling generally unwell but not being able to say why.

In elderly people a kidney infection may cause confusion. This is why a urine test is often done when an elderly person suddenly becomes confused and appears to be generally unwell.

Do I need any tests?

It is important to find out which bacterium (germ) is causing the infection. This will enable a doctor to prescribe the correct antibiotic. A urine sample is needed to identify the bacterium. This may be the only test that is needed for women who are otherwise healthy, but develop cystitis which progresses to a kidney infection. Further tests may be advised in some situations. For example, if a kidney stone or a kidney abnormality is suspected. Tests are also more likely to be advised for men and children, and for anyone with recurring kidney infections.

What causes a kidney infection?

A kidney infection can occur at any age. It is much more common in women.

• Most kidney infections develop as a complication from a cystitis (bladder infection). Bacteria causing cystitis sometimes travel up to infect a kidney. The bacteria are usually those which live in your bowel. They sometimes travel from the anus, up the urethra into the bladder, and cause infection. (Note: cystitis is common, and most people with cystitis do not develop a kidney infection.)
• Some kidney infections develop without a bladder infection. This is sometimes due to a problem in the kidney. For example, you are more prone to kidney infections if you have a kidney stone or an abnormality of a kidney.

What is the treatment for a kidney infection?

• Antibiotics will usually clear the infection. An antibiotic is usually prescribed straight away if a kidney infection is suspected, even before the result of the urine test is known. Some bacteria are resistant to some antibiotics. Therefore, sometimes you may need a change of antibiotic if the urine test shows a bacterium which is resistant to the initial antibiotic. The course of antibiotics is for 7 - 14 days, depending on which one is used.
• Painkillers such as paracetamol or ibuprofen ease pain and reduce a high temperature (fever). Stronger painkillers may be needed if the pain is more severe.
• Have lots to drink to prevent dehydration.

In many cases, the infection is not too severe and clears with a course of antibiotic tablets. However, some people are admitted to hospital. For example, if:

• the infection is severe, or
• does not settle quickly with antibiotics, or
• you are otherwise ill or frail, or
• you are at risk of dehydration due to vomiting a lot.

In hospital, antibiotics can be given straight into the vein for a more immediate effect. If you are dehydrated, you may also need a 'drip' (where fluid is put straight into a vein).

Most people who previously had normal kidneys make a full recovery if treatment is given promptly. Possible complications which occur in a small number of cases include the following.

• Permanent damage to the kidney. This is unusual if you have a normal kidney which becomes infected. However, repeated kidney infections are a complication of some kidney disorders which may damage the kidney further.
• Sometimes bacteria from a kidney infection get into the bloodstream, particularly if treatment is delayed. This may cause septicaemia (blood poisoning). This can be serious or even life-threatening.

© EMIS and PIP 2005   Updated: September 2005   PRODIGY Validated