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.
- Having a condition that blocks, or obstructs, your urinary tract, such as kidney stones.
- Having a condition that prevents you emptying your bladder fully, such as an injury to your spinal cord.
- Having a weakened immune system – for example, due to type 2 diabetes, or as a side effect of treatments that weaken the immune system, such as steroid tablets or chemotherapy.
- Having an infection of the prostate gland called prostatitis, because the infection can spread from the prostate gland into the kidneys.
- Being female and sexually active. This is because sexual intercourse can irritate the urethra and allow bacteria to travel more easily through it and into your bladder.
- Having a urinary catheter (a thin, flexible tube that's inserted into your bladder to drain away urine).
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:
- have prostatitis. Researchers have found that over 90% of men with a kidney infection also have a prostate gland infection
- have anal sex
Now, find out how kidney infections are diagnosed.
