Why do urinary tract infections happen?

Author: SCIRE Community Team | Reviewer: Bonnie Nybo | Published: 9 November 2018 | Updated: ~ Nov 9, 2018

Urinary tract infections happen when bacteria or other microorganisms enter the urinary tract and start to multiply and grow. Most UTIs are caused by bacteria like E. coli. However, fungi, viruses, and parasites can also cause infections.

Although anyone can experience a UTI, people with SCI have a greater risk of developing one because of changes to how the bladder works, catheterization which may be used to manage the bladder, and a number of other factors:

Learn the importance of cleanliness through Liander’s advice on hygiene.

What is E.coli?

Low-temperature electron micrograph of a cluster of E. coli bacteria, magnified 10,000 times.²

Escherichia coli (E. coli) is a species of bacteria which is commonly found in the lower intestine of mammals. There are many types of E.coli and most are harmless to us, or even beneficial, as they are part of the normal gut flora and can produce beneficial compounds that we absorb and by preventing pathogenic bacteria from moving in. However, while E. coli normally resides in the gut it does not normally reside in the bladder and is responsible for most UTIs.

If a person cannot fully empty the bladder, any bacteria that have entered into the urinary tract cannot be flushed out fully during emptying. The leftover urine in the bladder can create an environment that promotes growth of bacteria that can cause infection.

Overstretching of the bladder due to overfilling can damage the bladder walls, which increases the risk of infection. Overfilling can also cause reflux which causes the urine to back up to the kidneys (see below).

Reflux occurs when urine flows backwards from the bladder to the kidneys and can increase the risk of infection in the kidneys and ureters. It can be caused by detrusor sphincter dyssynergia, where the coordinated action of two muscles (the detrusor of the bladder and the sphincter of the urethra) is disrupted. Instead of relaxing when urinating, the sphincter muscle contracts. This interrupts the outflow of urine causing pressure in the bladder to rise, which can result in reflux.

Urinary catheters (thin tubes that can be inserted into the bladder) are often used to drain the bladder after an SCI. However, catheters can also increase risk of infections because they provide a pathway for bacteria to enter the urinary tract. A catheter can pick up bacteria from contact with skin and surfaces and bring it into the bladder when it is inserted. This is a greater risk if catheters are reused or techniques are not done hygienically.

Indwelling catheters can sometimes get blocked, which prevents urine flow and can cause urine to remain in the urinary tract for too long. This can allow bacteria to grow and multiply. Proper care of catheters is important to reduce contamination and avoid blockages. The indwelling catheter is a foreign object in the bladder and this can increase the risk of bacteria or bladder stone formation as well.

Most people also experience changes to bowel function after SCI which can cause bowel accidents and the need to perform regular bowel routines. This can lead to bacteria (often E. coli) from feces entering the urinary tract and causing infections.

Poor hygiene when performing a bladder routine, such as not washing the hands or genitals before inserting a catheter, not using sterile technique when inserting an indwelling catheter, or wearing condom catheters for longer than 24 hours without cleaning the genitals, especially, can allow bacteria to enter the urinary tract. In addition, wetness from a poorly managed bladder can increase the risk of infections spreading.

• Women are at greater risk for developing UTIs because female anatomy increases the risk of the natural bacteria from the vagina or anus to enter the urinary tract
• Older age (especially over 65) increases the risk of developing a UTI because of incomplete bladder emptying
• Obstruction of the urinary tract from something like a kidney or bladder stone, enlarged prostate, or narrowing of the urethra
• Sexual intercourse, including the use of protective equipment such as diaphragms or spermicides
• Other health conditions such as diabetes or conditions that reduce ability to fight infections such as HIV (human immuodeficiency virus)
• Reduced sensation, as sensation is one of the ways that early infections of the urinary tract are detected. This is usually experienced as pain when urinating or over the abdomen or back
• Other infections, such as infected wounds, can sometimes travel into the urinary tract
• Reduced functional abilities may result in difficulty performing clean technique in bladder management
• Reduced economic resources may result in reusing catheters or unclean environments or decreased care support
• Pregnancy
• Menopause
• Depression