A UTI is an infection of one or more parts of the urinary tract. The urinary tract consists of two kidneys, two ureters, a bladder, and a urethra. The kidneys are bean-shaped organs found in the lower back below the ribcage. They filter waste out of the blood and produce urine to carry the waste and excess water out of the body. The urine is carried through the ureters (tubes) from the kidneys to the bladder. The bladder is a hollow muscular organ that stores urine for a short time period. The bladder stretches as urine accumulates and at a certain point it signals to the body that it needs to relieve the growing pressure. A muscular valve (sphincter) at the opening of the bladder is relaxed and the bladder contracts to send urine through the urethra (a tube linking the bladder to the external surface of a person's skin) and out of the body.
A UTI is sometimes referred to by the part of the urinary tract affected. Inflammation of the urethra (usually due to an infection but sometimes due to irritation), is called urethritis. If the bladder becomes involved it is referred to as cystitis, and if the kidneys are inflamed it is called pyelonephritis. Frequently, the blanket term UTI will be used by your doctor, because there is not a simple test that can tell exactly how much of the urinary tract is infected.
Urine does not normally contain microorganisms, but if it is obstructed from leaving the body or retained in the bladder, it provides a good environment for bacteria to grow. Most urinary tract infections are due to bacteria that are introduced into the opening of the urethra. They stick to the walls of the urethra, multiplying and moving up the urethra to the bladder. Most UTIs remain in the lower urinary tract (urethra or bladder) where they cause annoying symptoms, such as a burning sensation during urination, but are more easily treated. While these infections are easily treated in most cases, if inadequately treated, the infection may spread up through the ureters, and into the kidneys. A kidney infection is more dangerous, and can lead to permanent kidney damage - especially in young children and the elderly, in those with diabetes and those with other underlying kidney diseases. In some cases a urinary tract infection may lead to an infection in the bloodstream (sepsis, septicaemia) that can be life-threatening. Rarely, a bloodstream infection can enter the kidneys and bacteria can enter the urine from this route.
Although a variety of bacteria can cause UTIs, most (80 to 90 percent) are due to Eschericia coli, a bacterium that is common in the gut and is routinely found in faeces. Other bacteria that may cause UTIs include species of: Proteus, Klebsiella, Enterococcus and Staphylococcus. Occasionally, a UTI may be due to a yeast, such as Candida albicans. Urethritis is often due to a sexually transmitted disease such as herpes, chlamydia, or gonorrhoea.
Although anyone at any age can have a UTI, women are much more likely than men to have them. It is thought that this is partly anatomical, because a woman’s urethra is shorter (less distance for bacteria to travel) and because their anus and vagina are relatively close to the urethra. Anything that slows down the passage of the urine, blocks it, or introduces bacteria into the urinary tract can raise a patient’s risk of having a UTI. Conditions that cause an increased risk for developing a UTI include:
- Anatomical problems (such as narrowing of the urethra or ureters)
- Urine retention (the bladder does not empty completely)
- Vesicoureteral reflux (the abnormal flow of urine from the bladder back to the ureters
- Kidney stones
- Bladder catheterisation (especially long term)
- Spinal cord injuries
- Diabetes (it causes changes to the immune system, damage to the kidneys and often results in sugar in the urine – promoting the growth of bacteria)
- Kidney disease
- Any condition that suppresses the immune system
- In men, an enlarged prostate may reduce the flow of urine.
What are the signs and symptoms?
Although UTI symptoms vary, many people will experience:
- A strong, persistent desire to urinate,
- A burning sensation during urination,
- A cloudy strong-smelling urine.
- Lower back pain
Those with UTIs may also have pressure in the lower abdomen and small amounts of blood in the urine. If the UTI is more severe and/or has spread into the kidneys, it may cause flank pain, high fever, shaking, chills, nausea or vomiting. Fevers are also seen when the infection spreads into the blood (sepsis). Some patients may also experience mental changes and confusion with a UTI, while others may not have any symptoms at all.
What are the complications?
In most cases UTIs are acute and uncomplicated. They are treated and the symptoms subside within a day or two. UTIs that spread to the kidneys, however, may cause permanent kidney damage, especially in the elderly and the very young. Conditions or diseases that result in chronic or recurrent UTIs may also damage to the kidneys and in some cases cause kidney failure. Kidney failure and sepsis (infection of the blood) can be life-threatening conditions. They require immediate treatment – which often involves hospitalisation. In pregnant women, a UTI can lead to premature labour and delivery and cause high blood pressure. In men, a UTI can cause prostate infection and inflammation, which can be difficult to treat.