What causes urinary tract infections (UTI)?

In 80-90% of cases of uncomplicated cystitis, Escherichia coli (E. coli) is involved. This bacteria is present in 70-95% of both upper and lower UTIs. Other common pathogens are Enterococcus faecalis, Klebsiella species, Proteus species.

What are the risk factors for urinary tract infections (UTI)?

The largest group of patients with UTIs is adult women. Women are more prone to UTIs than men because in females, the urethra is much shorter and closer to the anus.

The occurrence of UTI also varies with age. The incidence of UTI is ten times higher in adolescent girls as compared with boys and this continues throughout adult life.

Other predisposing factors include:

• Menopause. Rates of UTI are higher in postmenopausal women for a few reasons. For one, the presence of bladder or uterine prolapse can cause incomplete bladder emptying and stasis (reduced flow or stoppage of flow) of urine which in turn promotes the growth of pathogens. Also, the loss of oestrogen after menopause leads to changes in the vaginal flora, especially the loss of lactobacilli, and increases your susceptibility to infection.
• Sexual activity. UTIs are very common in women aged 18-30 years as UTIs are associated with coitus (the so-called ‘honeymoon cystitis’). In this age group, sexual intercourse is the cause of 75-90% of bladder infections, with the risk of infection being related to the frequency of sex. The use of spermicides and diaphragms for contraceptive purposes further increases the risk of UTIs as it causes a change in the vaginal flora and eradication of the vaginal lactobacilli.
• Recent instrumentation of the urinary tract (e.g., catheterisation, cystoscopy, urodynamic studies). The insertion of foreign instruments into the urinary tract promotes the translocation of bacteria colonised around the periurethral area into the bladder and other parts of the urinary tract. This increases the risk of developing bacteriuria (the presence of bacteria in the urine) in significant numbers eventually leading to a UTI.
  
• Foreign bodies (e.g., catheters, urinary stones). Urinary catheters are the most important risk factor for bacteriuria. Catheters introduce organisms into the bladder and promote colonisation by providing a foreign surface for bacteria to adhere to and by causing irritation of the bladder mucosa. 80% of UTIs that occur while in hospitals or healthcare institutions are related to urethral catheterisation, and 5-10% are related to manipulation of the genitourinary tract. Urinary stones similarly irritate the bladder as well as provide a nidus for bacteria to adhere to, thereby increasing the risk of developing a UTI.
• Neurological disorders, drugs or pelvic organ prolapse. These conditions may cause incomplete emptying of the bladder, thereby promoting stasis of urine which increases the risk of UTI development.
• Medical conditions (e.g., diabetes). Diabetes leading to glycosuria (sugar in the urine) makes for a fertile breeding ground for bacteria. A study showed that 9.4% of patients with type 2 diabetes had a UTI compared to only 5.7% of people without diabetes.
• Co-existing diseases involving the pelvis (e.g., tumours, inflammatory bowel disease).