Pyelonephritis is a bacterial infection of the kidney and the most serious form of urinary tract infection. If not diagnosed and treated early, repeated attacks of pyelonephritis can lead to permanent kidney damage resulting in hypertension and renal failure.
E. coli (Escherichia coli) is usually the bacteria causing a urinary tract infection. Most commonly the infection is mild and only affects the bladder (cystitis). Less commonly, the infection spreads up the ureters to affect the kidney (pyelonephritis). Pyelonephritis may be secondary to a renal tract abnormality that causes an obstruction to the normal flow of urine. This increases the chance that infection will spread to one or both kidneys.
Vesico-ureteric reflux, hydronephrosis and posterior urethra valves increase the chances that a urinary tract infection will result in pyelonephritis.