Bacteriuria can become bacteremia with associated systemic complications in the setting of urinary tract obstruction. Most bacteria enter the urinary tract system through the urethra from the fecal reservoir. In addition, the kidneys can be secondarily infected by Staphylococcus aureus or Candida by hematogenous spread. Escherichia coli (most common), Proteus, Klebsiella, and Enterococcus faecalis are frequently found to cause infection in the urinary tract.

When there is an increased pressure in the upper urinary tract, pyelovenous backflow may allow infected urine to enter the bloodstream. In addition, there is a change in renal blood flow and decreased neutrophil delivery. This is the proverbial “pus under pressure.” Clinical signs and symptoms of urinary tract obstruction are dependent on the time course of the obstruction, whether the obstruction is complete or unilateral, and the cause of the obstruction. Frequent symptoms include flank pain, nausea, and vomiting. Some clinical signs include rising blood urea nitrogen (BUN) or creatinine, electrolyte abnormalities, and hypertension.