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Alternate Names

  • kidney infection
  • Kidneys and adrenal glands


Pyelonephritis is an infection in the kidneys themselves.

What is going on in the body?

Escherichia coli is a bacterium that is normally found in the large intestine. It causes about 90 percent of kidney infections.
These infections usually spread from the genital area, more commonly in women, because they have a much shorter urethra (the tube from the bladder to the outside that passes urine) hooked to the bladder, and then up the ureters.
In a healthy urinary tract, the infection is prevented from going to the kidneys by the flow of urine, which washes organisms out. When bacteria enter the usually "germ-free" urinary tract, they can cause cystitis (most commonly) a bladder infection and/or pyelonephritis.


What are the causes and risks of the infection?

Pyelonephritis is usually caused by bacteria entering the kidneys from the ureters or the blood stream. The most common causes of bacteria reaching the bladder include:
  • use of a urinary catheter for draining urine from the bladder
  • surgery on the urinary tract
  • kidney stones
  • pregnancy
  • anything that blocks urine output like a big prostate gland in men or congenital situations like a "UPJ" obstruction (ureteropelvic junction obstruction) that does not allow the urine to drain properly
  • conditions that make a person more prone to infection, such as diabetes or medications that suppress the immune system (like methotrexate, for example).
  • pyelonephritis can also occur when bacteria enter the blood stream from another organ and infect the kidney secondarily (like with a heart valve infection).


What can be done to prevent the infection?

There are many ways to prevent the spread of bacteria in the urinary tract. These include:
  • wiping from the front to the back of the genital area, especially after a bowel movement
  • drinking plenty of fluids
  • emptying the bladder as possible after sexual intercourse (in women)
  • if a catheter to drain urine becomes necessary, removing it as soon as is possible
  • in women with frequent bladder infections, sometimes a short course of antibiotics can prevent a urinary tract infection
  • in diabetics controlling sugar levels
  • in patients with certain kidney diseases like polycystic kidney disease
According to the Natural Medicines Comprehensive Database, the daily consumption of cranberry juice 10 oz (300 mL) seems to prevent recurrent urinary tract infections (UTIs) in young and elderly women. A combination product containing cranberry juice plus alpine cranberry (Vaccinium vitis-idaea) also seems to prevention UTIs. But neither cranberry juice nor cranberry extract seem to prevent UTI in adults or children related to neurogenic bladder.
However, there's not enough evidence it for using cranberry juice to treat UTIs and there is little evidence that encapsulated forms of concentrated cranberry offer the same benefits as the juice.


How is the infection diagnosed?

Diagnosis requires a history, physical, and urinalysis. A urine culture is also done on a urine sample to see if there are bacteria in the urine and what kind of bacteria they are.
A test can be done to make that the bacteria are killed by the antibiotic chosen for treatment. A sample of blood is cultured in the same way as urine.
Typical findings in urine include pus or many white blood cells, and/or blood in the urine.
X-rays like an ultrasound or a CT scan may be done if there are complications (no response to antibiotics for 3 days, suspicion that there may be a kidney stone or an infection in a diabetic) are also helpful in the diagnosis and treatment.

Long Term Effects

What are the long-term effects of the infection?

Untreated pyelonephritis can lead to:
  • permanent kidney damage or loss of the kidney
  • scarring of the kidneys
  • sepsis, or blood poisoning and death

Other Risks

What are the risks to others?

Pyelonephritis is not contagious.


What are the treatments for the infection?

A person is usually given antibiotics as soon as the diagnosis of a kidney infection seems likely, but after the urine and blood cultures are obtained. For severe infections, initial treatment is usually given IV until the patient is afebrile for 48 hours. For less severe infections, oral antibiotics can be used.
The most common antibiotics prescribed include:
  • specific penicillins like ampicillin or amoxicillin (i.e., Amoxil, DisperMox, Trimox)
  • amoxicillin-clavulanate (i.e., Augmentin)
  • sulfa medications (like trimethoprim-sulfamethoxazole <i.e., Bactrim, Cotrim, Septra, Sulfatrim>)
  • cephalosporins, such as cefaclor (i.e., Ceclor) or cephalexin (i.e., Keflex)
  • ciprofloxacin (i.e., Cipro), moxifloxacin (i.e., Avelox), levofloxacin (i.e., Levaquin), norfloxacin (i.e., Noroxin), gatifloxacin (i.e., Tequin)
A person with a severe infection may need to be hospitalized. Sometimes surgery or tube placements in X-ray are needed to correct a physical problems with the urinary tract or remove an obstruction like a kidney stone.

Side Effects

What are the side effects of the treatments?

The side effects of antibiotics include stomach upset, rash, infection and colitis with a bacterium called C. difficile or allergic reactions. The side effects of surgery include bleeding, infection, or reactions to anesthesia.

After Treatment

What happens after treatment for the infection?

It is very important for the person to complete the full course of antibiotics. In some cases, a low dose of an antibiotic may be prescribed for a person to take continually to keep the infection from coming back.
Sometimes a person has many episodes of pyelonephritis in a short time period. Further testing may need to be done to rule out kidney disease or urinary tract abnormalities that cause an obstruction.
Common tests include:
  • ultrasound of the kidney and bladder
  • a CT scan
  • a voiding cystourethrogram, or VCUG, in which a liquid is put into the bladder through a catheter, or tube, inserted through the urethra. An x-ray then follows the liquid through the bladder and urethra. This test can reveal abnormalities of the inside of the urethra and bladder or abnormal flow of urine (up and back into the kidney instead of to the outside, called reflux).
  • intravenous pyelogram, which examines the whole urinary tract. A liquid is injected through a tube inserted into a vein. An x-ray then follows the liquid as it flows through the urinary tract. This test may reveal blockages in the tract. It has been essentially replaced by the CT scan.
  • a nuclear scan, in which radioactive materials are injected into a vein. This test shows how the kidneys work, how the kidneys are shaped, and how urine drains from the kidneys (this test can diagnose and follow "UPJ" obstructions and determine if surgery is necessary).


How is the infection monitored?

Usually, after treatment, the healthcare provider will recheck a urinalysis and urine culture to be sure the infection is resolved.
If antibiotics do not lead to improvement, ultrasound or CT may be used to check for an obstruction or an abscess.
Untreated pyelonephritis or pyelonephritis complicated by an obstruction, polycystic kidney disease, or an abscess can lead to very serious kidney damage or death.. Any new or worsening symptoms should be reported to the healthcare provider.


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Harrison's Principles of Internal Medicine, Fauci, 1998

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