Organisms that infect the urinary tract generally enter through the urethra and ascend toward the bladder. Although urinary tract infections (UTIs) do occur in males, they appear more commonly in females. Infection of the urinary bladder produces cystitis. The infecting organisms are usually colon bacteria carried in feces, particularly Escherichia coli. Cystitis is more common in females than in males because the female urethra is shorter than the male urethra and the opening is closer to the anus. Poor toilet habits and urinary stasis are contributing factors. In the hospital, UTIs may result from procedures involving the urinary system, especially catheterization, in which a tube is inserted into the bladder to withdraw urine.

Less frequently, UTIs originate in the blood and descend through the urinary system. An infection that involves the kidney and renal pelvis is termed pyelonephritis. As in cystitis, signs of this condition include dysuria, painful or difficult urination, and the presence of bacteria and pus in the urine, bacteriuria and pyuria, respectively. Urethritis is inflammation of the urethra, generally associated with sexually transmitted diseases such as gonorrhea and chlamydial infections.

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