Kidney Infection (cont.)

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What are the causes of kidney infection?

Urine, similar to other fluids in the body, is normally sterile without any bacterial infection. Therefore, the presence of bacteria in the urine is considered abnormal and may lead to urinary tract infection. Typically, bacteria gain access to the urinary system from outside through the urethra (the drainage tube for urine from the bladder). The bacteria may then ascend in the urinary system and cause kidney infections. Kidney infection (upper UTI) is typically more severe than lower UTI because bacteria may also infect the bloodstream (bacteremia) from the kidneys resulting in a more severe illness.

Bacteria may travel from the rectum or the vagina towards the urethra to gain entry into the urinary system. Other bacteria may enter from the skin. Women are more susceptible to urinary tract infections due to the shorter length of their urethras in comparison to those of men.

What are risk factors for kidney and urinary tract infection?

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There are many factors that may increase the chances for infection of the kidneys and urinary tract.

Premenopausal women are at higher risk for developing UTI and kidney infection. Risk factors within this population include:

  • Sexual intercourse (for women -- may increase the risk of urinary tract infection because of possible introduction of the bacteria around the urethra into the urinary system [a condition sometimes referred to as "honeymoon cystitis"])
  • Previous urinary tract infection
  • Use of spermicides
  • History of mother with recurrent UTIs (which suggests a possible genetic component to susceptibility)
  • Pregnancy

In fact, 2% to 8% of pregnant women may have urinary infections during their pregnancy. This may occur because of slower transit of urine in the ureters during pregnancy from the pressure applied by the enlarging uterus.

In postmenopausal women, physiological factors (vaginal dryness, urinary incontinence, urinary retention, and prolapse of the pelvic organs) seem to add potential risk to develop UTIs and kidney infections.

In men, prostate enlargement is the main risk factor for UTI and kidney infection.

Urinary catheters (Foley catheters) also increase the risk of developing urinary and kidney infections. These catheters are used in settings where an individual may not be able to urinate due to paralysis (neurogenic bladder), severe illness, bed bound state, incontinence of urine (inability to hold their urine), or bladder dysfunction. Urinary catheters simply provide a physical vehicle for the bacteria from outside to be directly transported into the bladder and the urinary system.

Kidney stones and other structural abnormalities of the urinary system may also cause kidney infection. Impaired draining and blockage of urine may cause bacteria to ascend to the kidney without being washed back down with the urine. Any obstruction to the flow of urine can serve as a focus of infection that can spread to other parts of the urinary tract.

Urinary stents placed in ureters to relieve obstruction due to stents or tumors are also a potential risk for kidney infection. As matter of fact, any instrumentation or procedure of the urinary system (stenting, cystoscopy, biopsy, and transurethral resection of the prostate (TURP) can pose a risk for infection of the urinary tract.

Diabetes mellitus may also increase the risk of kidney infection in both men and women.

In children, risk factors for kidney infection include female gender, uncircumcised male, structural abnormalities of the urinary tract, and Caucasian race (four times higher than African American).

Medically Reviewed by a Doctor on 7/5/2012

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