Causes and risk factors of urinary tract infection

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Factors that predispose people to the occurrence of urinary tract infection can occur from both the microorganisms involved and patients.  

Some germs are particularly aggressive and may be resistant to the antibiotics used to treat infections. This is because the widespread use and sometimes misuse of antibiotics have led to some bacteria becoming resistant to them.  

The range of factors that can promote urinary tract infections in patients is very wide.  

Decreased immune system cells seen under the microscope

Immunocompromised people. Due to diseases or medical treatments, these people have decreased defence against infections. Therefore, meticulous follow-up of these patients is required. 

Person with thin and thick intestine

Changes in the intestinal microbiota. The largest reservoir of germs with the potential to cause urinary tract infections is found in the intestine; these are called "intestinal microbiota" (previously "intestinal flora"). Changes in these microbiota due to changes in diet, for example, can increase the possibility of urinary infection. 

Woman with tummy ache next to the WC

Chronic diarrhoea or constipation can predispose a person to recurrent urinary tract infection, so controlling bowel movements is key to avoiding urinary tract infections. 

Vaginal infection and microbes

In women, changes in the vaginal microbiota are clearly related to urinary tract infection. Under normal conditions, vulvovaginal microbiota have a protective effect against urinary tract infection. The use of powerful soaps or disinfectants can remove vaginal microbiota and facilitate infection by pathogenic germs. For this reason, it is advisable to use mild soaps, such as those for small children, for feminine intimate hygiene, so as not to harm this protective flora. 

Also, the menopause can lead to atrophy of the vulvovaginal mucosa and changes in the microbiota. Therefore, many gynaecologists advise the use of oestrogen creams or ointments.  

Urinary incontinence in a woman

Post-void residual volume. This is one of the most important risk factors for urine infection. Post-void residual volume is the amount of urine left in the bladder of patients who do not empty it effectively when urinating. This increases the number of germs in the bladder, making urinary tract infection more likely. Post-void residual urine may be due to an obstruction or loss of strength in the bladder muscles. 

Kidneys and urinary system

Some anatomical abnormalities of the urinary system (e.g. diverticula, lithiasis, malformations or vesicoureteral reflux) can lead to a growth in bladder microbiota and infection. 

Person with urinary catheter

The presence of vesical probes or catheters within the urinary system can result in increased bacterial growth and urinary infection. This is due to a kind of mucus produced by bacteria (biofilm) that grows around external objects inserted into the body, such as a probe. 

Crossed-out water bottle

The kidneys of people who take in small amounts of liquid are forced to concentrate the urine. This concentrated urine is rich in waste products and is a favourable environment for urinary infection. Patients with a tendency to suffer urinary tract infections are advised to drink about 8 glasses of water a day (or 2 litres). The type of water does not matter. 

icono mujer sentada en el WC, de perfil

Some women deliberately practise intermittent urination under the false belief that this reduces the possibility of urinary incontinence later in life. Urination must be performed without these imposed behaviours, which can lead to post-void residual urine and promote infection. Another practice to avoid is squeezing your abdomen to urinate. Although it produces the sensation that it improves the way you urinate, it actually promotes the presence of post-void residual urine. 

Symbol of man and woman

During intercourse, for women it is easy for germs from the vulvar area to enter the bladder through the urethra. If there is also a change in vulvovaginal flora, this can trigger an infection. Sufficient lubrication during intercourse must be maintained and 2 glasses of water should be drunk afterwards, to rinse out any germs that could have entered the bladder during sex. Some women have cystitis frequently after intercourse. In these cases, and always under medical supervision, the use of an antibiotic before or after intercourse may be advisable.

Controlling these factors can decrease predisposition to urinary tract infection.  

Substantiated information by:

Agustín Franco
Ascensión Gómez Porcel
Pilar Luque
Verónica Rico Caballero

Published: 30 March 2022
Updated: 30 March 2022

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