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A General Overview, Etiology And Pathogenesis Of Urinary Tract Infections

Updated on February 6, 2014

Urinary Tract Infections

What Are The Signs And Symptoms Of Urinary Tract Infection?
What Are The Signs And Symptoms Of Urinary Tract Infection?

Etiology And Pathogenesis

The urinary tract is a common site for bacterial infections in humans. Women i=of child-breaing age are affected more. About 20% of all women develop urinary tract infection at sometime or other in their lives.

The term acute ‘pyelonephritis’ refers to acute inflammation of the kidney and its pelvis. In chronic pyelonephritis, there is inflammation of pelvis and calyces with fibrosis and deformity of renal parenchyma. Infection limited to the bladder is termed “cystitis”. Presence of more than 100,000 (105) pathogenic bacterial/ml of urine is ‘significant bacteriuria’. Sometimes significant bacteriuria may exist without producing symptoms- “asymptomatic bacteriuria”. Reflux nephropathy denotes the renal involvement which occurs as a result of vesico-ureteric reflux. Vesico-uretheric reflux is frequently caused or accompanied by bacterial infection.

Etiology: The organisms associated with urinary tract infection are those found most frequently in the gastrointestinal tract or in the vaginal vestibule. Approximately 80-85% are caused by Escherichia coli (E.Coli). Proteus, Klebsiella and Enterobacter species are relatively more common in hospital- acquired infections. Other organisms include Streptococcus fecalis, Pseudomonas aeruginosa and some species of Candida. The urine is strongly acidic in E.Coli infection. In Proteus infection, the urine is highly alkaline as a result of conversion of urea into ammonia in the urinary tract.

Pathogenesis: In many women there is a tendency for colonization of the organisms in the introitus. On account of the shortness of the urethra and tendency to produce lower urinary tract obstruction during pregnancy, women suffer more. Sexual intercourse serves to precipitate infection in predisposed individuals. Bacteria gain access to the urethral meatus from the anorectal regions and they ascend through the urethra or periurethral tissue into the bladder, ureters, renal pelvis, and parenchyma. Structural abnormalities of the urinary tract, obstructive lesions, presence of foreign bodies such as calculi or catherters, vesico-ureteric reflux, pregnancy and diabetes mellitus predispose to urinary infection.

Vesico-ureteric reflux is the pathological condition in which urine from the bladder regurgitates into the ureter and ascend to the Kidney during the process of micturition. Urinary tract infection is a common complication of vesico-ureteric reflux. A combincation of factors such as the back pressure transmitted from the bladed and persistence of infection leads to renal acarring and chronic interstitial nephritis.

Host defence against bacteria depends on the integrity of the phagocytes and the immune system. Local protective factors are the constant downward flow of urine and periodic evacuation of the bladder, the pH of urine, and prostatic secretions in males. Hematogenous infection of the urinary tract, through relatively rare, may occur as part of septicemia or in immunosuppressed hosts.

Urinary Tract Infections



In acute pyelonephritis, the kidneys are enlarged and contain several small abscesses. Areas of inflammation may be seen. With very severe infection, the bases of renal papillae may undergo necrosis and detached fragments may be passed in urine. These may cause acute ureteric obstruction or even reflex anuria. Histologically, the interstitium shows edema and patchy infiltration by polymorphonuclear leucocytes. The glomeruli are relatively normal.

In chronic pyelonephritis, the kidneys are often smaller than normal and their surfaces showing scarring. The renal calyces may show abnormalities on account of scarring. The corticomedullary junction may be indistinct and the renal cortex itself may be thinned out. Histological features are tubular damage, infiltration of the interstitium with chronic inflammatory cells, fibrosis and scarring. Glomeruli may show areas of focal sclerosis.

© 2014 Funom Theophilus Makama


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