Understanding the urinary tract
There are two kidneys - one on each side of the tummy (abdomen). They make urine which drains down tubes called ureters into the bladder. Urine is stored in the bladder and is passed out of the bladder through a tube called the urethra, when we go to the toilet.
What is a urine infection and what causes it?
Most urine infections are caused by germs (bacteria) that come from your own bowel. They cause no harm in your bowel but can cause infection if they get into other parts of your body. Some bacteria lie around your back passage (anus) after you pass a stool (faeces). These bacteria sometimes travel up the tube called the urethra and into your bladder. Some bacteria thrive in urine and multiply quickly to cause infection.
A urine infection is often called a urinary tract infection (UTI) by doctors. When the infection is just in the bladder and urethra, this is called a lower UTI. If it travels up to affect one or both kidneys as well then it is called an upper UTI. This can be more serious than lower UTIs, as the kidneys can be damaged by the infection.
Why do some people develop urine infections?
In many cases the infection occurs for no apparent reason. There is no problem with the bladder, kidney, prostate, or defence (immune) system that can be identified. In other cases, an underlying problem can increase the risk of developing a urine infection.
In older women
- After the menopause the lining of tissues around your genital area may become more fragile. This is called atrophic vaginitis. It is associated with having more urine infections.
- A prolapse of the womb (uterus) or vagina can also increase your risk of infection.
In older men
An enlarged prostate may stop the bladder from emptying properly. Some urine may then pool in the bladder. Germs (bacteria) are more likely to multiply and cause infection in a stagnant pool of urine. See separate leaflet called Prostate Gland Enlargement for more details.
- Bladder or kidney problems may lead to infections being more likely. For example, kidney stones or conditions that cause urine to pool and not drain properly.
- Having a thin, flexible, hollow tube (called a catheter) in place to drain urine.
- An underlying health condition may also be responsible. A poor immune system increases the risk of having any infection, including urine infections. For example, if you are having chemotherapy to treat cancer. Diabetes can also increase your risk of having urine infections.
- Being constipated. If your lower gut (bowel) is full and swollen, it may press on the bladder. This may stop it emptying properly, making you more prone to urine infection.
Further reading and references
Management of suspected bacterial urinary tract infection in adults; Scottish Intercollegiate Guidelines Network - SIGN (updated July 2012)
Guidelines on Urological Infections; European Association of Urology (2015)
Urinary tract infection (lower) - women; NICE CKS, July 2015 (UK access only)
Urinary tract infection (lower) - men; NICE CKS, October 2014 (UK access only)
Rowe TA, Juthani-Mehta M; Urinary tract infection in older adults. Aging health. 2013 Oct9(5). doi: 10.2217/ahe.13.38.
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