Complicated urinary tract infections (UTIs) occur in the setting of a urinary tract that has metabolic, functional, or structural abnormalities. Complicated UTIs may involve both lower and upper tracts .Their primary significance is that they significantly increase the rate of therapy failures.
The pathophysiology of complicated UTIs has the following 4 aspects:
Structural abnormalities, such as calculi, infected cysts, renal/bladder abscesses, certain forms of pyelonephritis, spinal cord injury (SCI), and catheters
Metabolic/hormonal abnormalities, such as diabetes and pregnancy
Impaired host responses, such as transplant recipients (especially renal transplants) and patients with AIDS
Unusual pathogens, such as yeast
A growing number of complicated UTIs are healthcare associated in origin. The most common pathogens include Escherichia coli, enterococci, Pseudomonas aeruginosa, candidal species, and Klebsiella pneumoniae.
Pyelonephritis is almost always the result of bacteria migrating from the bladder to the renal parenchyma, which is enhanced by vesicourethral reflux. In uncomplicated pyelonephritis, the bacterial invasion and renal damage are limited to the pyelocalyceal-medullary region; in complicated pyelonephritis, all regions of the kidney may be affected. If the infection progresses, bacteria may invade the bloodstream, resulting in bacteremia.