UTI Causes: How Do You Get it & Who is at Risk?
1. Quick insights about what causes UTI:
- Bacteria commonly cause UTIs. The most frequent bacteria are E. coli.
- Bacteria is usually derived from poop and travels to the urinary tract from the outside through the urethra.
- UTI is more common in females.
- UTI can be simple, uncomplicated cystitis (urinary bladder infection) or severe and complicated (with a kidney infection and systemic symptoms.
- The most common risk factors include frequent sexual intercourse, spermicide-coated diaphragms, condoms, and diabetes mellitus.
- Recurrent simple cystitis (frequent UTIs) is very common in young and healthy women.
2. ROUTE: How does infection reach your urinary tract?
To understand how the urinary tract happens, you should learn some basic anatomy about your urinary system.
The Urinary system consists of:
- The organ that filters blood and makes urine (the Kidneys).
- The tube delivers urine from the kidneys to the urinary bladder (the ureters).
- The hollow organs act as a temporary storage site for urine until you pee (the urinary bladder).
- The tube carries urine from the bladder to the outside of your body when you pee (the urethra):
- In females, the urethra is shorter and wider (making the female bladder more exposed to the outside bacteria).
- In males, the further is significantly longer and narrower (making males less vulnerable to UTI).
A. The common route (urethra).
Bacteria is the most common cause of UTIs. However, other organisms, such as fungi and viruses, may also infect your urinary tract.
Your urinary tract is originally sterile (it doesn’t contain bacteria). However, bacteria often infect the urinary tract by entering the urethral opening and traveling inwards to reach the urinary bladder.
The following sequence happens:
- Bacteria often comes from your colon (stool).
- The bacteria often colonize at the urethral meatus (the opening through which you pee).
- Then they travel to the inside of the urinary tract through the urethra.
Simple UTI (cystitis):
After reaching the urinary bladder, bacteria commonly stop at this stage, causing the most common type of UTI (acute cystitis or simple UTI) (reference).
Complicated UTI (Pyelonephritis):
Less commonly, bacteria may continue to travel upwards in the urinary tract causing infection of the kidney itself (which is a more severe form).
The kidney infection by bacteria ascending through the ureter is a complicated UTI (called pyelonephritis).
MORE: Urethral Irritation: Causes & How Long Does it Last?
B. The rare route (through the bloodstream).
In rare cases, The bacteria reach the urinary tract through the bloodstream. For example, this occurs in severe infections with bacteria circulating in the bloodstream (bacteremia).
My thoughts as a doctor:
More than 95% of the time, UTIs occur in females as uncomplicated cystitis. The most common route is bacteria from the poop reaching the urinary bladder through the urethra.
3. ORGANISMS: What Organisms Cause UTI?
The most common bacteria are:
- E-coli is the most common cause of UTI (75% to 95% of the cases) (reference).
- Others (less common):
- Klebsiella pneumonia
- Proteus mirabilis.
- Staphylococcus saprophyticus.
- Group B streptococci.
4. RISK GROUPS: Who is at higher risk of UTI?
Risk factors include (reference):
- Females: UTI is extremely common in females due to:
- Shorter distances between the urethral opening and the bacteria (from poop).
- The area around the urethral opening is always moist.
- Hormonal changes with contraception and during pregnancy.
- Recent sexual intercourse.
- The use of spermicide-coated condoms or diaphragms.
- Diabetes mellitus.
- The use of urinary catheters.
- After a kidney transplant (mainly due to immunosuppressive drugs).
The following factors DO NOT increase the risk of UTI (reference):
- Daily beverage consumption.
- Frequency of urination.
- The habit of delayed voiding.
- Tampon Use.
- Use of Hot tubs.
- Type of underwear.
- Obesity (High BMI).
6. COMPLICATED UTI: Who is at risk?
Uncomplicated UTI often refers to urinary tract infections confined to the lower urinary tract (urinary bladder).
The term “complicated UTI” refers to any UTI with any of the following features (reference):
- Fever >37.7°C (>99.9°F).
- Chills or rigors.
- Significant fatigue, muscle aches, or any other feature of systemic illness.
- Flank pain.
- Pelvic or perineal pain in men.
- Tenderness over the kidney area when your doctor examines it (tender costovertebral angle).
The following groups are at higher risk of developing complicated UTIs when they catch an infection.
- Presence of Stones in the Urinary bladder, kidney, or ureter.
- Obstruction inside the urinary tract (commonly ureteric, caused by a stone or a structure).
- Male gender.
- Diabetes mellitus.
- Chronic kidney disease (deteriorated kidney function).
- Immunosuppressive medications.
- Patients with spinal cord or neurological diseases (neurogenic bladder).
7. Causes of frequent (recurrent) UTIs.
As doctors, we define recurrent urinary UTI (mainly cystitis) as (reference):
- Two or more infections within six months, OR
- Three or more infections (UTIs) within one year.
Frequent UTIs are common among women, even young, healthy women with normal urinary tracts.
- 27% of women experience at least one recurrence of UTI within six months (reference).
- 2.7% will experience at least two recurrences within six months.
- Women with E. coli-induced UTIs are more likely to have recurrent UTIs than other causes (44% recurrence within one year (reference)).
Recurrent or frequent UTIs mainly occur as simple (uncomplicated) urinary bladder infections.
Main risk factors (reference):
- Behavioral risk factors.
- Being sexually active (the frequency of sexual intercourse is the strongest risk factor for recurrent cystitis (reference)).
- New sex partners.
- Diaphragm-spermicide use.
- Spermicide-coated condoms.
- Having the first UTI before or at the age of 15 years.
- Having a mother with a history of UTIs.
- Abnormal Urinary tract (especially in postmenopausal women).
- Urinary incontinence.
- Cystocele (dropped or prolapsed urinary bladder into the vaginal space).
- Post-voiding residual urine (incomplete voiding of the urinary bladder).
- Genetic or biological factors.
- Genetic predisposition to recurrent UTIs is obvious. For example, daughters of women with recurrent UTIs are at higher risk.