The urinary tract, from the kidneys to the urethral meatus, is normally sterile and resistant to bacterial colonization despite frequent contamination of the distal urethra with colonic bacteria. The major defense against urinary tract infection (UTI) is complete emptying of the bladder during urination. Other mechanisms that maintain the tract’s sterility include urine acidity, the vesicoureteral valve, and various immunologic and mucosal barriers.
About 95% of UTIs occur when bacteria ascend the urethra to the bladder and, in the case of pyelonephritis, ascend the ureter to the kidney. The remainder of UTIs are hematogenous. Systemic infection can result from UTI, particularly in older patients. About 6.5% of cases of hospital-acquired bacterimia are attributable to UTI.
Uncomplicated UTI is usually considered to be cystetitis or polynephritis that occurs in premenopausal adult women with no structural or functional abnormality of the urinary tract and who are not pregnant and have no significant comorbidity that could lead to more serious outcomes. Also, some experts consider UTIs to be uncomplicated even if they affect postmenopausal women or patients with well-controlled diabetes. In men, most UTIs occur in children or older patients, are due to anatomic abnormalities or instrumentation, and are considered complicated.
The rare UTIs that occur in men aged 15 to 50 years are usually in men who have unprotected anal intercourse or in those who have an uncircumcised penis, and they are generally considered uncomplicated. UTIs in men this age who do not have unprotected anal intercourse or an uncircumcised penis are very rare and, although also considered uncomplicated, warrant evaluation for urologic abnormalities.
Complicated UTI can involve either sex at any age. It is usually considered to be pyelonephritis or cystitis that does not fulfill criteria to be considered uncomplicated. A UTI is considered complicated if the patient is a child, is pregnant, or has any of the following:
- A structural or functional urinary tract abnormality and obstruction of urine.
- A comorbidity that increases risk of acquiring infection or resistance to treatment, +