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Kidney (Renal) Infection (Pyelonephritis)

Infection of one or both kidneys by bacteria is the condition called pyelonephritis.

What happens under normal conditions?

The kidneys function to remove waste products from your body as urine. Urine travels from the kidneys to the bladder where it is excreted via the urethra. The kidneys in their healthy state are sterile, that is they are not infected with bacteria. However, bacteria can infect the kidneys, usually by entering the urethra and ascending into the bladder (causing cystitis or urinary tract infection) and from the bladder continuing their ascent into the kidneys.

Cystitis is very common in females, occurring in 1-3% of adult women per year. Extension of a bladder infection to the kidneys to cause pyelonephritis is less common (about 1 in every 30 cases of urinary tract infection) but more severe. Pyelonephritis risk is increased during pregnancy, with obstruction of the urinary system (from a kidney stone for example), with abnormalities of the urinary system (seen in young girls but also in adults due to diverticula and other abnormalities), with diabetes, and with a weakened immune system.

What are the signs of pyelonephritis?

The symptoms of pyelonephritis are pain and tenderness in the flank (the part of the back between the ribs and the hip) with fever, and usually with frequent, urgent and/or painful urination. Nausea and vomiting are common. Much less common are lightheadedness, confusion or loss of consciousness due to sepsis and shock (this can occur if bacteria enter the bloodstream from the kidney) in the most severe form of pyelonephritis.

Because it can be life threatening it is important for you to seek immediate medical care should you have symptoms that suggest pyelonephritis. Many other problems in the pelvis and abdomen can cause symptoms that mimic pyelonephritis, such as kidney stones or appendicitis for example; so one of the first steps that your health care provider will take is to determine if your urine is infected.

Why does pyelonephritis happen?

Pyelonephritis usually happens because bacteria enter the urethra where they travel to the bladder to cause cystitis and from there into the kidney. Cystitis is very common in females, occurring in 1-3% of adult women per year. Extension of a bladder infection to the kidneys to cause pyelonephritis is less common (about 1 in every 30 cases of urinary tract infection) but more severe. Pyelonephritis risk is increased during pregnancy, with obstruction of the urinary system (from a kidney stone for example), with abnormalities of the urinary system (seen in young girls but also in adults due to diverticula and other abnormalities), with diabetes, and with a weakened immune system.

What are treatment options for pyelonephritis?

Pyelonephritis is treated with antibiotics. In many cases orally administered antibiotics will suffice, but with severe infection and/or with nausea and vomiting that precludes taking medicines by mouth hospitalization and intravenous antibiotics may be required until the patient recovers enough to take oral antibiotics. In order to eradicate the infection and prevent relapse a prolonged treatment course is required, usually a total of 2 weeks or more of antibiotics. Surgery may be needed if an obstruction in the urinary track is discovered (most patients when admitted to the hospital for pyelonephritis will receive an ultrasound examination of the kidneys to look for obstruction).

What can be expected after treatment for Pyelonephritis?

Improvement in the symptoms is seen within one to several days with effective antibiotic therapy in the absence of obstruction. If there is obstruction then a urologic procedure to relieve the obstruction (due to a stone or a structural abnormality in the urinary tract) is usually required for treatment. Even though the symptoms are gone within several days, completion of the entire two or more week treatment with antibiotics is required to prevent the infection from relapsing.

In the case of frequent recurrences of pyelonephritis a small dose of antibiotic may be administered every day to prevent recurrences.

Frequently asked questions:

Will pyelonephritis damage the kidneys? Yes untreated pyelonephritis can damage the kidneys and lead to renal insufficiency or less commonly complete renal failure. This can occur both due to direct infection-related damage of the kidney as well as secondary damage from inadequate blood flow to the kidney if sepsis occurs.

Are the bacteria that cause pyelonephritis resistant to antibiotics? Yes the bacteria can be resistant to some antibiotics, but it would be very unusual for it to be resistant to all antibiotics. Both urine and blood cultures are taken prior to starting antibiotics; these can help the health care provider to change the therapy based on the sensitivity of the infecting bacteria to different antibiotics.

What can I do to avoid getting pyelonephritis? Women should wipe from the front to the back after having a bowel movement, as this will help to prevent the introduction of the bacteria that cause cystitis and pyelonephritis into the urethra. Urinating after sexual intercourse may help to flush out any bacteria introduced into the urethra. The use of forms of contraception other than diaphragms and spermicidal foam may help, as these kinds of contraception can cause more frequent urinary tract infection.

What if I am pregnant? Urinary tract infections during pregnancy are dangerous for both the mother and baby and should be treated immediately. There are many antibiotics that are safe to use even during pregnancy that can cure the infection.



Reviewed: January 2011

Last updated: April 2013

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Kidney (Renal) Infection Glossary
  • abdomen: Also referred to as the belly. It is the part of the body that contains all of the internal structures between the chest and the pelvis.

  • abnormality: A variation from a normal structure or function of the body.

  • antibiotic: Drug that kills bacteria or prevents them from multiplying.

  • appendicitis: Swelling of the appendix causing severe pain.

  • bacteria: Single-celled microorganisms that can exist independently (free-living) or dependently upon another organism for life (parasite). They can cause infection and are usually treated with antibiotics.

  • bladder: The bladder is a thick muscular balloon-shaped pouch in which urine is stored before being discharged through the urethra.

  • bladder infection: Also known as cystitis. Urinary tract infection involving the bladder. Typical symptoms include burning with urination, frequency, urgency and wetting.

  • bowel: Another word for intestines or colon.

  • bowel movement: The act of passing feces (stool) through the anus.

  • culture: Biological material grown under special conditions.

  • cyst: An abnormal sac containing gas, fluid or a semisolid material. Cysts may form in kidneys or other parts of the body.

  • cystitis : Inflammation of the bladder, causing pain and a burning feeling in the pelvis or urethra.

  • cystitis: Also known as bladder infection. Urinary tract infection involving the bladder, which causes inflammation of the bladder and results in pain and a burning feeling in the pelvis or urethra.

  • diabetes: A medical disorder of increased blood sugar levels that can cause bladder and kidney problems.

  • diaphragm: A curved muscular membrane that separates the abdomen from the area around the lungs.

  • diverticula: Plural of diverticulum. A pouch or sac in the lining of the mucous membrane of an organ.

  • excrete: Expel liquid and solid waste from the body.

  • flank: The area on the side of the body between the rib and hip.

  • immune system: The body's system for protecting itself from viruses and bacteria or any "foreign" substances.

  • infection: A condition resulting from the presence of bacteria or other microorganisms.

  • intravenous: Also referred to as IV. Existing or occurring inside a vein.

  • intravenous antibiotics: Medicine inserted directly into the veins.

  • ions: Electrically charged atoms.

  • kidney: One of two bean-shaped organs that filter wastes from the blood and discharge these waste products in urine. The kidneys are located on either side at the level of the 12th ribs toward the back. The kidneys send urine to the bladder through tubes called ureters.

  • kidney stone: A stone that develops from crystals that form in urine and build up on the inner surfaces of the kidney, in the renal pelvis or in the ureters. (Also see nephrolithiasis.)

  • kidneys: One of two bean-shaped organs that filter wastes from the blood and discharge these waste products in urine. The kidneys are located on either side at the level of the 12th ribs toward the back. The kidneys send urine to the bladder through tubes called ureters.

  • nephritis: Inflammation of the kidneys.

  • obstruction: something that obstructs, blocks, or closes up with an obstacle

  • pelvis: The bowl-shaped bone that supports the spine and holds up the digestive, urinary and reproductive organs. The legs connect to the body at the pelvis.

  • pregnancy: The condition of being pregnant.

  • pyelonephritis: Also referred to as kidney infection usually caused by a germ that has traveled up through the urethra, bladder and ureters from outside the body. Typical symptoms include abdominal or back pain, fever, malaise and nausea or vomiting.

  • renal: Pertaining to the kidneys.

  • renal failure: Loss of the kidney's ability to excrete wastes, produce urine and conserve electrolytes.

  • sepsis: Presence in blood or other body tissues of harmful bacteria spreading from a focal point of infection.

  • sperm: Also referred to as spermatozoa. Male germ cells (gametes or reproductive cells) that are produced by the testicles and that are capable of fertilizing the female partner's eggs. Cells resemble tadpoles if seen by the naked eye.

  • spermicidal foam: A contraceptive method to kill sperm, the male reproductive cells that are produced by the testicles.

  • sterile: Incapable of becoming pregnant or inducing pregnancy.Can also mean free from living germs or microorganisms.

  • stone: Small hard mass of mineral material formed in an organ.

  • ultrasound: Also referred to as a sonogram. A technique that bounces painless sound waves off organs to create an image of their structure to detect abnormalities.

  • urethra: A tube that carries urine from the bladder to the outside of the body. In males, the urethra serves as the channel through which semen is ejaculated and it extends from the bladder to the tip of the penis. In females, the urethra is much shorter than in males.

  • urge: Strong desire to urinate.

  • urinary: Relating to urine.

  • urinary tract: The system that takes wastes from the blood and carries them out of the body in the form of urine. Passageway from the kidneys to the ureters, bladder and urethra.

  • urinary tract infection: Also referred to as UTI. An illness caused by harmful bacteria, viruses or yeast growing in the urinary tract.

  • urination: The passing of urine.

  • urine: Liquid waste product filtered from the blood by the kidneys, stored in the bladder and expelled from the body through the urethra by the act of urinating (voiding). About 96 percent of which is water and the rest waste products.

  • urology: Branch of medicine concerned with the urinary tract in males and females and with the genital tract and reproductive system of males.

  • void: To urinate, empty the bladder.

Kidney (Renal) Infection Anatomical Drawings

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