Anatomical, structural and functional abnormalities are risk factors for urinary infection.
A common consequence of an anatomic abnormality is vesicoureteral reflux, which is present in 30-45% of young children with symptomatic forms of urinary tract infection. Vesicoureteral reflux is usually due to a birth defect that causes vesicoureteral valve incompetence.
Vesicoureteral reflux can also be acquired in patients with flaccid bladder or spinal cord injury or as a result of urinary tract surgery.
Other anatomical abnormalities that predispose to urinary tract infections include urethral valves (congenital obstructive anomaly), delayed maturation of the bladder neck, bladder diverticula, and urethral duplications (see Overview of Congenital Genitourinary Abnormalities).
Structural and functional abnormalities of the urinary tract that predispose to urinary tract infections are usually related to an obstructed urinary flow and inadequate bladder emptying.
Urinary flow can be compromised by stones and tumors. Bladder emptying can be compromised by neurogenic dysfunction, pregnancy, uterine prolapse, cystocele and prostatic hypertrophy. UTIs caused by congenital factors most commonly occur in childhood. Most other risk factors are more common in the elderly.
Other risk factors for UTI include instrumentation (eg, bladder catheterization, stent placement, cystoscopy) and recent surgery.
Etiology
- The bacteria that most often cause cystitis or pyelonephritis are the following:
- Enteric bacteria, usually aerobic Gram-negative (most often)
- Gram-positive bacteria (less often)
In a normal genitourinary tract, strains of Escherichia coli with specific adhesion factors for the transitional epithelium of the bladder and ureter are involved in 75-95% of cases. Other Gram-negative urinary pathogens are typically Enterobacteria, typically Klebsiella or Proteus mirabilis, and occasionally Pseudomonas aeruginosa.
Among the Gram-positive bacteria, Staphylococcus saprophyticus is isolated in 5-10% of bacterial infections of the urinary tract. Gram-positive bacteria such as Enterococcus faecalis (group D streptococci) and Streptococcus agalactiae (group B streptococci) are less commonly isolated and may be contaminants, particularly if they have been isolated from patients with uncomplicated cystitis.
In hospitalized patients, E. coli accounts for approximately 50% of cases. Gram-negative species Klebsiella, Proteus, Enterobacter, Pseudomonas and Serratia account for about 40%, and Gram-positive cocci E. faecalis, S. saprophyticus and Staphylococcus aureus account for the other cases.
Urethritis
Infection of the urethra caused by bacteria (or protozoa, viruses or fungi) which occurs when the microorganisms that reach it acutely or chronically colonize the numerous periurethral glands present in the bulbar and penile urethra in the male and in the entire urethra in women.
The sexually transmitted pathogens Chlamydia trachomatis (see Chlamydial, Mycoplasma and Ureaplasma Infections), Neisseria gonorrhoeae (see Gonorrhea), Trichomonas vaginalis (see Trichomoniasis) and herpes simplex virus are the most frequent causes in both sexes.