What is a kidney infection?

Kidney infection (pyelonephritis) is an upper urinary tract infection (UTI) that generally begins in your urethra or bladder and travels up into your kidneys. Most kidney infections start out as common bladder infections.

If not treated properly and promptly, a kidney infection can permanently damage your kidneys or the bacteria can spread to your bloodstream and cause a life-threatening infection. Fortunately, kidney infections can almost always be cleared up with a full course of antibiotics.

Some kidney infections can develop without a bladder infection and are due to a problem within the kidney itself. As an example, people with kidney stones or an abnormality of the kidney are more susceptible to kidney infections.

What causes a kidney infection?

Often, the bacteria that cause a kidney infection are the same as those that cause ordinary urinary tract infections. Bacteria found in bowel (such as E. coli or klebsiella) are the most common type. In rare cases, kidney infections can be caused from bacteria found on the skin or in the environment.

Bacteria enter the body from the skin around the urethra. They then travel up the urethra to the bladder. A kidney infection happens when the bacteria escape the urethra and bladder and travel up the ureters to one or both kidneys. Usually it is only one kidney that develops an infection.

Sometimes, conditions that create a reduced urine flow can contribute to kidney infections. Mainly because bacteria can more easily travel up the ureters when urine flow slows or stops altogether.

A kidney infection can occur at any age and is much more common in women than men. This is because women are more at risk of developing a bladder infection, which can then spread to the kidneys. This happens because a woman’s urethra is closer to the anus allowing bacteria to be easily introduced from the bowel and to travel up the urethra.

Other common ways bacteria can find its way into the bladder include:

• use of a urinary catheter for draining urine from the bladder
• surgery on the urinary tract
• diagnostic testing that uses a scope to enter the urinary tract, such as cystoscopy
• conditions that block the way the urine flows through the urinary tract, such as uterine fibroids, benign prostatic hyperplasia, kidney stones, and pregnancy
• conditions that make a person more prone to infection, such as diabetes
• a problem with the urinary tract that is present at birth

What are the symptoms of a kidney infection?

Most kidney infections start with a bladder infection which can include symptoms like:

• Pain when the bladder fills, and throughout the pelvic area
• The need to urinate frequently (sometimes up to 40 times a day)
• The overwhelming urge to urinate, even after you’ve just done so
• Cloudy, bloody or smelly urine

If the infection subsequently moves from the bladder to the kidneys, you may also experience infection symptoms like:

How is a kidney infection diagnosed?

The simple way to determine if you have a kidney infection is by urinalysis, which is the testing of a urine sample for bacteria, blood and pus. A urine culture may also be performed to test for the presence of bacteria or other organisms. Doctors can also diagnose kidney infections based on the above signs and symptoms.

Other tests might include an ultrasound, computerised tomography scan or a type of X-ray called a voiding cystourethrogram.

How is a kidney infection treated?

Antibiotics are usually prescribed for kidney infections. The type of antibiotic your doctor prescribes and for how long is dependent on the severity of your condition and the bacteria found in your urine tests.

Symptoms of a kidney infection often begin clearing up within a few days of treatment. However, you should still take the entire course of antibiotics to make sure the infection is completely eliminated.

In rare cases, you may require hospitalisation for a severe kidney infection where you’ll receive antibiotics intravenously (giving medicines or fluids through a needle or tube inserted into a vein. How long you’ll stay in the hospital will depend on the severity of your condition. 

Sometimes an underlying medical problem, such as a kidney abnormality can cause recurrent kidney infections. You may be referred to a kidney specialist (nephrologist) or urinary surgeon (urologist) to determine whether urologic abnormalities may be the cause and whether surgery is needed to repair the abnormality.

Complications from a kidney infection

Full recovery is expected after a treating a kidney infection with antibiotics, However, in rare cases complications can occur including:

• Bacteria from a kidney infection getting into the bloodstream, particularly if treatment is delayed. This can cause blood poisoning (septicaemia) and can be potentially life-threatening
• The development of a kidney abscess — a collection of pus that forms within the kidney (very rare)
• Permanent damage to kidney tissues

The above complications are rare but may become more likely if:

• You become severely ill with the kidney infection
• You already have other problems with your kidneys, like polycystic kidney disease, reflux or kidney failure
• You have kidney stones
• Your immune system is suppressed — for example, if you have cancer, if you’re taking medication such as steroids or chemotherapy, or if you have AIDS
• You have poorly controlled diabetes
• You are over 65 years old

Another rare complication is Emphysematous pyelonephritis where kidney tissues are rapidly destroyed by the infection and the bacteria releases toxic gases that build up inside the kidneys. It tends to affect people who have poorly controlled diabetes and is a very serious illness.

Can a kidney infection be prevented?

As most kidney infections start with a bladder infection, the same preventative measures to reduce your chances of bladder infection should also reduce your chances of a kidney infection.

Top tips to prevent further kidney infections

Some of the things that may help include the following:

• Don’t hold your urine. Go to the toilet promptly
• Stay well hydrated and make sure you drink plenty of fluids every day
• Constipation can increase your chances of a bladder or kidney infection, so treat constipation promptly
• Empty your bladder after having sex
• Always make sure that you wipe from front to back after going to the toilet
• Avoid using feminine products such as deodorant sprays or douches in your genital area

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