Kidney infection (pyelonephritis) is an infection of the kidney and the ducts that carry urine away from the kidney. The infection usually begins when bacteria enter the urinary tract through the urethra or bladder and travel up into the kidneys.
The urinary system is composed of the kidneys, ureters, bladder, and urethra. Each plays a role in removing waste from the body. The kidneys filter waste from blood, adjust blood levels of many substances, and conserve or excrete water from the system. Tubes called ureters carry urine from the kidneys to the bladder, where it's stored until it exits the body through the urethra.
Kidney infection can be classified as acute (sudden development) or chronic (a long-standing infection that does not clear). If not treated properly the infection can permanently damage your kidneys or spread to your bloodstream and cause a life-threatening infection, so be sure to contact your health care provider as soon as symptoms appear.
Kidney infection is more common in women than in men.
The risk of developing a kidney infection is increased if there is a history of urinary tract infection as well as a history of renal papillary necrosis (death of some or all of the renal papillae), kidney stones (a solid mass that consists of a collection of tiny crystals), vesicoureteric reflux (persistent backflow of urine from the bladder into the ureters and kidneys), or obstructive uropathy (blockage of the flow of urine).
Other risk factors for kidney infection are the same as that of a urinary tract infection and include:
Escherichia coli (E.coli) - bacteria found in the lower gastrointestinal tract that causes 90% of kidney infections.
In both men and women:
Interference with the flow of urine with conditions such as an enlarged prostate in men or stone in the bladder.
Changes in the immune system with conditions such as cancer, diabetes, and AIDS or medications that lower the immunity such as high doses of corticosteroids.
Those who have had a urinary catheter placed in them for a surgery or diagnostic test or those who need prolonged use of bladder catheters such as the elderly or those who are bed ridden.
Anatomy - with a shorter urethra than men, bacteria doesn't have to travel as far to reach the bladder.
Sexual Intercourse - bacteria can be pushed into the urethra during intercourse.
Pregnancy - hormonal changes may increase a woman's risk.