Urinary tract infection (UTI)
Last Review Date: December 30, 2018
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 persons skin) and out of the body.
A UTI can be due to infection in any part of the urinary tract. The most common type is infection involving the bladder (also known as cystitis). If the infection then spreads to the kidneys it is called pyelonephritis.
Urine does not normally contain microorganisms, but if urine is obstructed from leaving the body or retained in the bladder, it provides a good environment for 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 which is a more serious condition which in rare cases can cause permanent kidney damage and needs a longer course of antibiotics. In some cases a urinary tract infection may lead to an infection in the bloodstream (septicaemia) that can be life-threatening.
Although a variety of bacteria can cause UTIs, most (80 to 90 percent) are due to Escherichia coli, a bacterium that is common in the gastrointestinal tract and is routinely found in stool (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 (infection involving the urethra) 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 through the ureters
- Kidney stones
- Bladder catheterisation (especially long term)
- Spinal cord injuries (leads to the inability of normal bladder emptying)
- 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)
- Any condition that suppresses the immune system
- In men, an enlarged prostate may inhibit the flow of urine.
Although UTI symptoms vary, many people will experience:
- A strong, persistent desire to urinate,
- Increased frequency of urination,
- A burning sensation during urination,
- A cloudy strong-smelling urine.
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 (septicaemia). Some patients may also experience mental changes and confusion with a UTI, while others may not have any symptoms at all.
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 children and the elderly if the infections are recurrent.
In some circumstances, urinary infections and sepsis (infection of the blood) can be life-threatening conditions requiring hospitalisation and immediate treatment.
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.
Common Laboratory Tests
Most UTIs are detected by performing a urinalysis and then confirmed with a urine culture. If there are bacteria present, then susceptibility testing is done to make sure that the antibiotic that the doctor chooses will effectively treat the causing the infection.
Urinalysis. A clean catch (midstream) sample collection is important to minimize sample contamination with skin cells and non-pathogenic bacteria. White blood cells (WBC, leukocytes), red blood cells (RBC), nitrites, and bacteria in the urinalysis may indicate a UTI.
Urine Culture. Urine is streaked on a thin layer of nutrient gel (agar plate), then incubated for 24-48 hours. Any bacteria that grow on the agar are counted and identified. Usually, if a person has a UTI, there will be a high colony count of one type of that will be present and susceptibility testing is done (sometimes the doctor may refer to it as “sensitivity” testing). If there are three or more types of bacteria present (or in a woman if there is normal vaginal bacteria present), the sample is considered to be contaminated, usually due to inappropriate collection method (i.e. not a midstream sample) and no further work is done on the culture. A repeat sample may need to be submitted if the person's symptoms persist.
Follow-up Laboratory Tests
If a doctor suspects that a UTI may have spread into the bloodstream, he/she may order a blood culture. If they suspect that a person’s symptoms may be due to a sexually transmitted disease, such as chlamydia or gonorrhoea, then they may test for one or more STDs.
In the case of recurrent or urinary tract infections, other laboratory tests such as glucose (to check for diabetes) or urea and creatinine (to evaluate kidney function) may also be done.
Blood Culture. Two samples of blood are taken to look for any bacteria in the blood, which is normally sterile. The blood samples are incubated in a broth culture medium at body temperature and examined at regular intervals for bacterial growth. Although most infections will be detected within 24-48 hours, some organisms may take longer to grow. When a person is septic from a urinary tract infection, the same microorganism is found in both the blood and the urine cultures. Susceptibility testing will provide information on which antibiotic will eradicate the from both the blood and the urine.
Imaging scans and special X-rays may also be used to look for anatomical problems and/or signs of an underlying disease or condition. If a person has recurrent or chronic UTIs, one or more of the following procedures may be ordered. Each gives the doctor different information.
Kidney and bladder ultrasound - uses sound waves to determine the structures of the bladder and the kidney; they can be seen as light and shadowed areas.
Voiding cystourethrogram (VCUG) - an x-ray test that examines the urethra and bladder while the bladder fills and empties
Kidney and bladder CT scans- a scan (commonly known as a CAT scan) that uses multiple beams of x-rays to give detailed views of the structures of the urinary tract to look for evidence of kidney infection or abscess along with any blockages in the urinary tract. May also allow visualisation of the structures of the pelvis.
Nuclear scans - several types may be used to examine the function and shape of the bladder and kidneys. For each scan type, a radioactive dye is injected into a vein. The dye is carried to the bladder and kidney, allowing the visualization of any structural abnormalities.
Cystoscopy - a flexible tube about the diameter of a straw is threaded up the urethra and into the bladder. It allows a doctor to look at the surface of the inside of urethra and bladder. It can help identify blockages and abnormalities. If a stone is present, other instruments can be inserted up through the cystoscope that may allow a stone to be removed or broken into smaller pieces with a laser. The crushing of these stones is called lithotripsy. Urine and tissue sample can also be taken using the cystoscope.
Intravenous pyelogram (IVP) - used to look at the whole urinary tract. An opaque dye is injected into a vein, then travels to the kidney and bladder. A series of x-rays are taken, which may reveal obstructions or structural abnormalities.
Prevention of a UTI centers on keeping the urine moving through the urinary tract and avoiding bacterial contamination of the urethra. Recommendations include:
- Drink plenty of water every day to flush out the urinary system
- Urinate as needed; don’t hold urine in for extended periods of time
- After a bowel movement, wipe from front to back to keep stool bacteria away from the urethra
- Avoid irritants to the urethra – avoid bubble baths if prone to recurrent UTIs, take showers instead of baths, and rinse soap off thoroughly
- Urinate after sexual intercourse; this may help rinse out any bacteria that may have come in contact with the urethra
- Avoid tight clothing and wear cotton underwear – it breathes and won’t trap moisture like some synthetic fibres
- Drink cranberry juice – some doctors recommend this to patients who have recurrent UTIs. It may help prevent bacteria from sticking to the walls of the urethra.
A UTI is usually treated with a course of antibiotics. The type, concentration, and length of drug therapy will depend on:
- Which specific bacteria is/are present
- What drugs the bacteria is/are susceptible to
- How much of the urinary tract is involved e.g. kidney or prostate involvement will require a longer duration of antibiotic therapy
- The health/allergies of the infected person
- Whether or not the person is having recurrent UTIs
- Whether the infection is acute or chronic
- Whether the antimicrobial is being used as a preventive measure or to treat an existing infection
- Whether the infection has spread to the blood
- Whether they are pregnant and what trimester they are in
If someone is particularly prone to recurrent infections and/or particularly vulnerable to kidney damage, his or her doctor may recommend preventive antimicrobials, on a continuing basis or early (prophylactic) treatment at the first sign of an infection occurring.
If an infection is due to a sexually transmitted disease, such as chlamydia or gonorrhea, the doctor will prescribe specific drugs that have been proven to be effective against these organisms. If a person is sexually active and experiencing recurrent UTIs, it may be due to an infection in his or her partner. In some cases, both partners will need to be treated. If a woman is on oral contraceptives, she may want to talk to her doctor as some antimicrobials can lessen their effectiveness.
If a woman is on antimicrobial therapy for several days, there is a chance that she may develop diarrhea or a vaginal yeast infection. This is because the drugs also kill good/normal bacteria and upset the balance of bacteria in the body. If this happens, additional treatment may be required.
Sometimes recurrent or chronic UTIs will occur until an underlying structural abnormality, stone, obstruction, or disease or condition is addressed. For some conditions, surgery may be required to correct the underlying problem
On this site
Tests: Urinalysis, urine culture, blood culture
Conditions: Kidney diseases, diabetes
Elsewhere on the web
Healthdirect Australia: Urinary Tract Infections
Kidney Health Australia: Urinary tract infections
Better Health Channel: Urinary tract infections
Health Navigator NZ: Urinary Tract Infection
Familydoctor.org: Urinary tract infections