What Causes Kidney Infection?

Although the urinary system is designed to keep bacteria out, problems can occur. Escherichia coli (E. coli) or other bacteria found in the intestines can enter the urinary tract through the urethra. These bacteria can travel up into the bladder. When this happens it can cause cystitis (inflammation of the bladder). It can also cause a urinary tract infection (UTI). Cystitis occurs in 1-3% of adult women per year. If the infection continues up to the kidneys, it can cause kidney infection. This problem is rare but it can be severe. About 1 in every 30 cases of UTI leads to a kidney infection.

You are more likely to get a kidney infection if you have frequent bladder infections or have a structural problem in the urinary tract. Urine normally flows only in one direction—from the kidneys to the bladder. If the flow of urine is blocked or flows in the wrong direction, infections can happen. Urine flow can be blocked by many things, including:

  • kidney stones,
  • tumors inside or outside the urinary tract and
  • structural problems of the urinary tract.

People with diabetes or a weak immune system are at high risk for infections. Pregnant women with UTIs should be seen by their health care provider and treated as soon as possible. A kidney infection in a pregnant woman can be very serious.