Pyelonephritis (kidney infection) Dr Rob Hicks Pyelonephritis means inflammation of the kidney, which is a commonly caused by a bacterial infection

In this article

What is pyelonephritis? Symptoms

Causes and risk factors Treatment and recovery

This infection results in a severe painful illness that can lead to scarring of the kidney.

Symptoms usually come on over a few hours or a day and include:

• Loin or back pain, often severe.
• Fever and shivers.
• Foul-smelling and cloudy urine which may be blood-stained.
• Nausea and vomiting.
• Sometimes there is painful and frequent urination.

Pyelonephritis is most common among children, pregnant women, those with diabetes and the elderly, who are all more likely to have predisposing factors. Women are more likely to suffer than men.

The bacteria that cause pyelonephritis usually get into the body through the urethra (the tube that urine passes through from the bladder). From here, they can move into the bladder (where they may initially establish an infection) and then up to the kidneys.

In women, the bacteria may get in during sex or if the anal area is wiped from back to front rather than front to back as recommended (allowing bacteria normally present in the bowels to spread to the urinary system). It may also happen in both men and women when catheterisation (a tube inserted into the bladder) is needed for medical reasons.

Anything that obstructs the normal flow of urine will interrupt the processes that naturally flush the system and allow bacteria to multiply in the stagnant urine. For example, enlargement of the prostate gland in men may be responsible for the blockage, or kidney stones.

In pregnant women the growing uterus can also compress and obstruct the urinary system, so women are now routinely screened during pregnancy for bacteria in the urine.

In children, structural abnormalities which allow urine to reflux back from the bladder up the ureters towards the kidneys are usually to blame.

People with poorly controlled diabetes experience sugar in the urine which allows any bacteria present to thrive.

If the bacteria are already inside the body (causing infection elsewhere, for example), then they may find their way to the kidneys as they are carried in the bloodstream.

Pyelonephritis needs to be taken seriously – if untreated it may prove fatal (especially in the elderly). Even when treated it can cause kidney scarring. Up to 15 per cent of children who have had a urinary tract infection with fever will have some degree of renal scarring.

When pyelonephritis is suspected, a urine specimen is tested to establish whether bacteria are present. If this is confirmed, treatment with antibiotics is necessary. If someone is very unwell, they may need to be admitted to hospital to be given intravenous therapy.

It’s always important to try to establish whether there are underlying factors which have lead to the infection.

Tests such as scans and x-rays and an assessment of kidney function are usually recommended once the infection has settled. This is especially true among boys and men where pyelonephritis is less common. If the attacks are recurrent or there are other complications then women are also offered these investigations.

As with all infections affecting the urine or kidneys, once the treatment has been completed it's important a further urine sample is tested to confirm the bacteria has been eradicated.

Its also important top take steps to try to prevent further infections (especially if someone has already experienced repeated infections). Advice includes simple steps such as good hygiene and front-to-back wiping after opening the bowels, and emptying the bladder after sex. Women using a diaphragm and spermicide for contraception may need to try a different method.

Cranberry juice has been found to contain a chemical which helps to stop bacteria sticking to the urinary system so a daily glass may be helpful. In some cases low dose antibiotic therapy may be recommended for several months.

This article was last medically reviewed by Dr Trisha Macnair in July 2009.