Urinary Tract Infection (UTI)

Urinary Tract Infection (UTI)

What is a urinary tract infection (UTI)?

A urinary tract infection (UTI) is characterised as an infection that occurs anywhere along the urinary (pronounced YOOR-uh-ner-ee) tract which includes the bladder, urethra, ureters (pronounced yoo-REE-ters) and kidneys. Infections can affect individual sections or multiple portions of the urinary tract.

Illustration showing the human urinary system including the kidneys, ureters, urinary bladder, and urethra.

Infection types are categorised according to their location in the urinary tract and include:

Lower urinary tract infections

  • Infection of the urethra which is known as urethritis.
  • Infection of the bladder that is referred to as cystitis (the most common form of UTI in women).

Illustration showing urethritis

Illustration showing the urinary bladder - normal and unhealthy lining with cystitis.

Upper urinary tract infections

  • An infection that progresses upstream and into the kidneys (one or both) can be very painful and is known as pyelonephritis (pronounced as pahy-uh-loh-nuh-FRAHY-tis).

Illustration showing normal kidney and chronic pyelonephritis.

One of the primary causes of UTIs is bacteria in the urinary tract, the most common of which is E coli. This bacterium is responsible for between 70 and 95% of all upper and lower urinary tract infections.

While it is not uncommon for bacteria to enter the urinary tract, usually any bacteria that does occur is easily flushed out of the body when a person urinates. A one-way flow of urine typically aids in keeping a build-up of bacteria away from the ureters, bladder and kidneys. Sometimes, however, bacterial colonisation occurs in the urinary tract causing an infection and the body’s natural defence mechanisms cannot easily flush out the offending organisms.

UTIs are not regarded as  severe or life-threatening conditions as these types of infections are generally manageable and can be relatively easily treated with no complications if appropriate treatment is sought timeously. However, infections which reach the kidneys can result in numerous health complications, quickly becoming serious.

Once affecting the kidneys, an infection can necessitate hospitalisation. Treatment will need to focus on reducing damage to the organs as much as possible and preventing functional problems, scarring or organ failure. Elevations in blood pressure (high blood pressure or hypertension) can also occur. An acute infection of one or both kidneys, along with bacterial leakage into the bloodstream can result in a potentially life-threatening condition (i.e. septicaemia - pronounced as sep-tuh-SEE-mee-uh). Sepsis can affect the whole body and requires immediate medical treatment.

How does the urinary tract work?

Illustration showing the urinary system

Essentially the urinary tract is the drainage system which expels urine from the body. Normal urination requires this system to function efficiently in the correct order – starting with the kidneys, then moving downwards from the ureters to the bladder and finally the urethra:

  • The kidneys: Two bean-shaped organs situated just below the rib cage, on each side of the spine, the kidneys filter between 113 and 142 litres (or 120 to 150 quarts) of blood every day. (1) They are non-stop working organs that process blood up to 300 times every day. (2) This filtering process produces approximately 0.95 to 1.9 litres (or 1 to 2 quarts) of urine (a liquid by-product of metabolism). Waste-products like urea, uric acid, salts and amino acids, as well as additional water not needed by the body are filtered from the blood in the form of urine which is removed from the body via the urinary tract.
  • The ureters: These are thin tubes or ducts which transport urine from the kidneys to the urinary bladder where it can be stored before being excreted via urination.
  • The bladder: Situated in the pelvis, between the pelvic bones, is the bladder – a hollow, balloon-shaped muscular organ which expands as urine is deposited into it via the ureters. The frequency with which a person feels the urge to urinate (empty the bladder) is dependent on how quickly the filtering process produces urine, filling the bladder. The bladder can hold between 1.5 to 2 cups (355ml to 473ml) of urine at any given time. (3) While filling up, the bladder wall muscles remain relaxed, and then nerves begin sending signals to the brain when this organ is almost full to capacity. These signals trigger the need to find a toilet and empty the bladder of urine. Did you know? - The bladder is the most common portion of the urinary tract to experience infections. (4) When the bladder becomes inflamed as a result of infection, this is medically referred to as cystitis.
  • The urethra: The emptying of the bladder and expulsion of urine from the body occurs through the urethra, which is situated at the base of the bladder. Three sets of muscles are involved in the process of urination – the first being where the urethra meets the bladder neck, the second within the bladder neck (internal sphincter) and the third located in the pelvic floor (external sphincter). The internal sphincter aids in keeping urine that accumulates in the bladder. The external sphincter helps to provide support to the urethra. The three sets of muscles work together, keeping urine in the bladder between emptying. The urge to urinate signals the muscles in the bladder wall to tighten up and the sphincters to relax, resulting in the emptying of the bladder as urine is squeezed out of the body via the urethra. In men, the urethra continues through the penis, while in women, it ends just above the opening to the vagina.

Why is healthy urinary tract function important?

As the ‘drainage system’, the urinary tract is an important filtering system for the body and along with healthy kidney function, helps to… (5)

  • Prevent an accumulation of waste products and excess fluids.
  • Maintain sufficient levels of electrolytes, like phosphate and potassium.
  • Regulate blood pressure by responding to necessary hormones (such as vasopressin – an antidiuretic hormone which is secreted by the pituitary gland in the brain, helping the kidneys to reabsorb necessary water back into circulation by concentrating urine, reducing urine output).
  • Generate red blood cells (through the production of erythropoietin (EPO), a protein that stimulates the bone marrow to make red blood cells).
  • Maintain strong bone structures through ensuring a healthy balance of minerals (Calcium and Vitamin D) in the blood which are required for bone density and strength.

Bacteria in urine is not uncommon and typically exists even without causing an infection. Within a healthy urinary tract, urine has several antibacterial properties which have a natural suppressing effect on infection. The pH levels, urea concentration (osmolarity) and presence of organic acids typically help to flush out much of the bacteria present, preventing its survival (or potential for growth) in the urinary tract, thus warding off infection.

Urinary tract infections as they affect gender and age groups

Urinary tract infections can occur in both males and females, of any age. UTIs are, however, most common in females. One reason for this is because the urethra in females is shorter than in males and located closer to the anus, allowing infection causing organisms easier access and thus increasing susceptibility to more frequent infections.

1. Paediatric UTIs

Urinary tract infections are common in children and generally only affect little girls. If a little boy has a urinary tract infection, every effort must be made to exclude a possible structural abnormality within the urinary tract.

It is important to remember that the ability to hold urine in the bladder and voluntarily pass this waste fluid is a learned process. Infants and toddlers (up to the age of 2 and a half years) are not able to voluntarily control the emptying process. (6)

From 27 months of age onwards, the pelvic floor muscles begin to stabilise, and the brain learns to work with the nerve cells of the bladder and develops the ‘control function’ necessary to prevent involuntary urinations. With age, a child’s bladder control becomes a more voluntary process, allowing the little one to get to a bathroom in time in order to urinate without having an emptying accident. The production of vasopressin becomes a little more fine-tuned as well, allowing the hormone to sufficiently decrease urine output (as it travels through the bloodstream and into the kidneys) so that the bladder does not fill up too quickly – this helps to ensure that a child does not awaken as frequently during the night with a full bladder, needing the bathroom or having nightly emptying accidents. By the age of 5, a young child should have improved daytime bladder control.

The most common variations of UTI affecting infants and children are:

  • Upper UTI / pyelonephritis (i.e. kidney infection)
  • Lower UTI / cystitis (i.e. bladder infection)

In rare instances, paediatric UTIs can occur as a result of an underlying structural urinary tract abnormality. Such abnormalities may be identified and diagnosed fairly soon after birth once the first signs of infection are evident. Some damage to the kidneys can occur if the condition is not diagnosed and treated in time. If treatment is implemented timeously, major kidney function impairments are not likely to occur.

2. UTIs in women

Lower urinary tract infections, particularly cystitis, is a common complaint for many females. A medical work-up will generally identify the presence of bacteria in the urine (known as bacteriuria) or yeast (known as candiduria).

If urine enters and accumulates in the bladder, bacterial proliferation (growth) can occur, resulting in cystitis (a bladder infection).

Women are especially vulnerable to UTIs during pregnancy, largely due to a variety of hormonal and mechanical changes that take place within the body during this time. Such changes increase a woman’s risk factors for experiencing difficulties in bladder emptying (a condition known as urinary stasis) or a backward flow of urine from the bladder to the kidneys (known as vesicoureteral reflux) as a result of functional changes of the muscles in the bladder and ureters. Difficulty in maintaining proper hygiene which increases the risk of bacterial entry can also make a woman more susceptible to UTI as her uterus grows throughout the gestation period.

A woman must be mindful of possible infections during her pregnancy as this can have an adverse effect on both herself and a growing foetus. The primary concerns are the development of pyelonephritis (a kidney infection) in the mother, along with a low birth weight, preterm birth or death of the foetus / infant (before or after birth). At the first signs of infection, symptoms must be appropriately diagnosed and treated to avoid these potential complications.

3. UTIs in men

UTIs are more common in men from the age of 50 onwards. This is mainly due to the following factors, some of which are more prevalent in men at this stage of life:

  • Prostatitis (swelling of the prostate)
  • Epididymitis (inflammation of the epididymis – a tube at the back of the testicle responsible for storing and carrying sperm)
  • Orchitis (inflammation of the testicles)

Types of infections which occur include:

  • Pyelonephritis (kidney / upper urinary tract infection)
  • Cystitis (bladder / lower urinary tract infection)
  • Urethritis (infection of the urethra)

Another common reason for UTIs in men are:

  • Urinary catheters (particularly during the later years or if affected by incontinence)

The male anatomy provides better defence against UTIs than that of females, making men less susceptible to infections. The male urethra is not located as close to the rectum or anus as the female urethra is (i.e. the distance is several centimetres longer). The male urinary tract sees flow of urine from the kidneys to an elastic bladder. The male bladder is able to store larger volumes of urine at lower pressures.

While less common than those encountered by females, males can also be affected by both lower and upper urinary tract infections and related conditions.

The most common urinary tract infections among males include:

  • Lower UTI: prostatitis, epididymitis, cystitis and urethritis
  • Upper UTI: pyelonephritis

Uncomplicated versus complicated urinary tract infections

Urinary tract infections are classified as either uncomplicated or complicated. At the time of onset of acute symptoms, it is impossible to definitively classify the type of infection being experienced by a patient. Doctors will thus consider various factors in order to determine this. Making a distinction between the two is essential is it will influence both pre- and post-treatment examination and testing and the extent to which these need to be carried out as well as the type of medication prescribed.

What is an uncomplicated UTI?

An uncomplicated UTI is the result of bacterial invasion of a usually health and normal urinary tract. This causes an infection of the urinary tract and its associated symptoms.

What is a complicated UTI?

A ‘complicated UTI’ is an infection that is associated with an underlying congenital abnormality, health condition or disease. This can include conditions wherein notable anatomic or structural abnormalities are evident that may require some surgical intervention in order to prevent further health complications or problems. Or there may be metabolic or hormonal and functional abnormalities present. Such abnormalities will typically involve both the upper and lower urinary tracts and impair the drainage function of the urinary tract.

Complicated UTIs may also involve the presence of, or colonisation by, pathogens like yeast or bacteria. Such pathogens can sometimes impact the effectiveness of the therapies implemented, rendering them less effective.

Structural / anatomical abnormalities can include:

  • Infected cysts
  • Calculi (these solid particles or stones within the urinary tract typically affect those with recurrent UTIs as a result of bacterial infection)
  • Abscesses of the bladder or kidneys (perinephric abscess, renal corticomedullary abscesses and renal cortical abscesses / renal carbuncles)
  • Pyelonephritis (focal pyelonephritis, also known as acute focal bacterial nephritis or acute lobar nephronia, and severe chronic infections known as xanthogranulomatous pyelonephritis)
  • A spinal cord injury
  • Abnormalities that develop as a result of an indwelling catheter (a thin tube / medical device that is inserted into the urethra to drain the bladder in the treatment of certain conditions)
  • Pelvic-ureteric obstruction
  • Ureteric and urethral strictures
  • Bladder diverticuli
  • Tumours
  • Polycystic kidney disease

Metabolic / hormonal abnormalities relate to conditions influenced by changes within the body and can include:

  • Pregnancy (ureter obstructions, muscle relaxation of the ureters and bladder, bacterial proliferation due to slightly reduced immunity, aminoaciduria / high amino acid content in urine, and glycosuria / high sugar content in urine)
  • Diabetes (high urine glucose content, increased intracellular calcium levels, and actin / protein interference can all contribute to vesicourethral reflux and recurrent UTI infections)

Other factors which may result in complicated UTIs include:

  • Organ transplants (particularly kidney transplants) and diseases such as AIDS may leave the individuals in question with impaired immune function.
  • The presence of resistant pathogen strains, like yeast (candida species), and bacteria such as Escherichia coli (E. coli), enterococci, Pseudomonas aeruginosa, and Klebsiella pneumoniae.
  • Individuals with a neurogenic bladder (problems stemming from the nervous system), bladder diverticulum (bladder outlet obstruction), and bladder or uterine prolapse – resulting in incomplete bladder emptying, placing a person at higher risk of bacterial accumulation.

Male UTIs are generally considered a kind of complicated UTI due to the anatomical differences of the urinary tract from those of women. This may impact how UTIs are treated in comparison to those of females. Acute uncomplicated UTIs can also occur in men as a result of infection due to anal intercourse or in those who have not been circumcised.

Kidney infections (pyelonephritis) can be both complicated and uncomplicated. 


1. National Institute of Diabetes and Digestive and Kidney Diseases. The Urinary Tract & How It Works: https://www.niddk.nih.gov/health-information/urologic-diseases/urinary-tract-how-it-works [Accessed 28.03.2018]

2. PubMed Health. 7 January 2015. How does the urinary system work?: https://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0072568/ [Accessed 28.03.2018]

3. National Institute of Diabetes and Digestive and Kidney Diseases. September 2013. Urinary Diversion - What is urinary diversion?: https://www.niddk.nih.gov/health-information/urologic-diseases/urinary-diversion [Accessed 28.03.2018]

4. National Institute of Diabetes and Digestive and Kidney Diseases. Bladder Infection (Urinary Tract Infection—UTI) in Adults: https://www.niddk.nih.gov/health-information/urologic-diseases/bladder-infection-uti-in-adults [Accessed 28.03.2018]

5. National Institute of Diabetes and Digestive and Kidney Diseases. The Urinary Tract & How It Works: https://www.niddk.nih.gov/health-information/urologic-diseases/urinary-tract-how-it-works [Accessed 28.03.2018]

6. Johns Hopkins Medicine. Toilet Training: https://www.hopkinsmedicine.org/healthlibrary/conditions/pediatrics/toilet-training_90,P02300  [Accessed 28.03.2018]

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