tract infection

Chapter 54 Urinary tract infection




Questions


image What are the main risk factors for the development of urinary tract infection?

image What is the difference between acute and chronic pyelonephritis?

Infection of the urinary tract is a common disease. If it involves the kidneys, it can cause renal failure. Normally, the bladder and upper urinary tract are sterile, although commensal organisms are found in the distal urethra. Host defence mechanisms that keep the bladder and upper urinary tract free of infection include regular evacuation of the bladder, which helps to eliminate any organisms that gain access to the bladder lumen; tight junctions between cells of the transitional epithelium, which act as a mechanical barrier; and resident inflammatory cells in the mucosa, including plasma cells that secrete IgA.




Aetiology and pathogenesis


By far the most common route of infection is via the urethra. These ascending infections are caused by organisms derived from the patient’s own faecal commensals that gain access to the urethra. Escherichia coli is the most frequent, but any faecal organism can be responsible. Sometimes, sexually transmitted organisms such as Neisseria gonorrhoeae cause ascending infections.


Any of the factors that predispose to infection in general increase the risk of urinary tract infection (Ch. 16). There are also factors specific to the urinary tract, which will predispose to ascending infection (Fig. 3.54.1).


Stasis of urine. If there is incomplete emptying of the bladder at each micturition, there will be a failure to clear the bladder of any contaminating organisms. This occurs in bladder outflow obstruction, as seen in urethral stricture, bladder tumours at the internal urethral orifice and nodular hyperplasia of the prostate, or when the nerve supply to the bladder is interrupted thus preventing normal contraction of the detrusor muscle.

Foreign body. The most common foreign body in clinical practice is a urinary catheter. Like any foreign body, a catheter can act as a focus for infection by providing a site where bacteria can multiply in a place protected from host defence mechanisms. Furthermore, catheterization can introduce microorganisms from the anterior urethra into the bladder. Another structure that can act as a foreign body is a urinary stone. Whether in the bladder or upper urinary tract, stones can act as a nidus of infection.
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Jul 3, 2016 | Posted by in MUSCULOSKELETAL MEDICINE | Comments Off on tract infection

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