Urine, similar to other fluids in the body, is normally sterile without significant 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 urinary tract infection) is typically more severe than lower urinary tract infection because bacteria may infect the bloodstream (bacteremia) from the kidneys.
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 the urethra.
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