Most urinary tract infections (UTIs) involve only the bladder and urethra (the lower urinary system). Pyelonephritis results when a UTI progresses to involve the upper urinary system (the kidneys and ureters).
The kidneys filter the blood to produce urine. Two tubes called the ureters carry urine from the kidneys down to the bladder. Urine travels from the bladder out of the body through the urethra.
Urethritis is inflammation of the urethra. That's the tube that carries urine from the bladder to outside the body.
Pain with urination is the main symptom of urethritis. Urethritis is commonly due to infection by bacteria. It can typically be cured with antibiotics.
Pyelonephritis may cause noticeable changes in the urine, such as:
Blood in the urine (hematuria)
Cloudy or foul-smelling urine
Pain when urinating
Increased frequency or urgency of urination
Causes of Pyelonephritis
Most often, the bacteria that cause pyelonephritis are the same as those that cause ordinary urinary tract infections. Bacteria found in stool (such as E. coli or klebsiella) are most common. Uncommonly, bacteria from the skin or the environment cause pyelonephritis.
Conditions that create reduced urine flow make pyelonephritis more likely. When urine flow slows or stops, bacteria can more easily travel up the ureters. Some causes of urine obstruction include: