Kidney infection (pyelonephritis)

Alternative names
Urinary tract infection - complicated; Infection - kidney; Complicated urinary tract infection; Pyelonephritis

Pyelonephritis is an infection of the kidney and the ducts that carry urine away from the kidney (ureters).

Causes, incidence, and risk factors

Pyelonephritis most often occurs as a result of urinary tract infection, particularly in the presence of occasional or persistent backflow of urine from the bladder into the ureters or kidney pelvis (vesicoureteric reflux).

Pyelonephritis can be further classified as follows:

  • Acute uncomplicated pyelonephritis (sudden development of kidney inflammation)  
  • Chronic pyelonephritis (a long-standing infection that does not clear)  
  • Reflux nephropathy (an infection that occurs in the presence of an obstruction)

Although cystitis (bladder infection) is common, pyelonephritis occurs much less often. The risk is increased if there is a history of cystitis, renal papillary necrosis, kidney stones, vesicoureteric reflux, or obstructive uropathy.

The risk is also increased when there is a history of chronic or recurrent urinary tract infection and when the infection is caused by a particularly aggressive type of bacteria.

Acute pyelonephritis can be severe in the elderly and in people who are immunosuppressed (for example, those with cancer or AIDS).


  • Flank pain or back pain  
  • Severe abdominal pain (occurs occasionally)  
  • Fever       o Higher than 102 degrees Fahrenheit       o Persists for more than 2 days  
  • Chills with shaking  
  • Warm skin  
  • Flushed or reddened skin  
  • Moist skin (diaphoresis)  
  • Vomiting, nausea  
  • Fatigue  
  • General ill feeling  
  • Urination, painful  
  • Increased urinary frequency or urgency  
  • Need to urinate at night (nocturia)  
  • Cloudy or abnormal urine color  
  • Blood in the urine  
  • Foul or strong urine odor  
  • Mental changes or confusion *

* Sometimes in the elderly, mental changes or confusion are the only signs of a urinary tract infection.

Signs and tests
An examination may show tenderness on palpation (pressing) over the kidney.

  • A urinalysis commonly reveals white blood cells (WBCs) or red blood cells (RBCs).  
  • A urine culture (clean catch) or urine culture (catheterized specimen) may reveal bacteria in the urine.  
  • A blood culture may show an infection.  
  • An intravenous pyelogram (IVP) or CT scan of the abdomen may show enlarged kidneys with poor flow of dye through the kidneys. (IVP and CT scan of the abdomen can also indicate underlying disorders.)

Underlying abnormalities of the kidney predisposing a patient to acute pyelonephritis may be discovered by additional other tests and procedures, including the following:

  • Voiding cystourethrogram  
  • Renal ultrasound  
  • Renal scan  
  • Renal biopsy


The goals of treatment are control of the infection and reduction of symptoms. Acute symptoms usually resolve within 48 to 72 hours after appropriate treatment.

Due to the high mortality rate in the elderly population and the risk of permanent kidney damage, prompt treatment is recommended.

After obtaining a urine culture to identify the bacteria, antibiotics are selected to treat the infection.

Intravenous (IV) antibiotics may be used initially to control the bacterial infection if your infection is severe or you cannot take antibiotics by mouth. In acute cases of pyelonephritis, you may receive a 10- to 14-day course of antibiotics.

Chronic pyelonephritis may require long-term antibiotic therapy. It is imperative that you finish taking the entire course of prescribed antibiotics. Commonly used antibiotics include the following:

  • Sulfa drugs such as sulfisoxazole/trimethoprim  
  • Amoxicillin  
  • Cephalosporins  
  • Levofloxacin and ciprofloxacin

Kidney damage can result from these infections. The elderly, infants, and people with a compromised immune system are at increased risk for developing sepsis (a severe blood infection). Often, these people will be admitted to the hospital to receive frequent monitoring for potential problems and to receive IV antibiotics, additional IV fluids, and other medications as necessary.

In diabetic patients and pregnant women, as well as in people with spinal paralysis, follow-up should include a urine culture at the completion of antibiotic therapy to ensure that bacteria are no longer present in the urine.

Expectations (prognosis)
Most cases of pyelonephritis resolve without complication after the treatment. However, the treatment may need to be aggressive or prolonged. If sepsis occurs, it can be fatal.


  • Recurrence of pyelonephritis  
  • Perinephric abscess (infection around the kidney)  
  • Sepsis  
  • Acute renal failure

Calling your health care provider
Call your health care provider if symptoms suggesting pyelonephritis occur.

If you have pyelonephritis, call your health care provider if new symptoms develop, especially decreased urine output, persistent high fever, or severe flank pain or back pain.


Prompt and complete treatment of cystitis (bladder infection) may prevent development of many cases of pyelonephritis. Chronic or recurrent urinary tract infection should be treated thoroughly because of the chance of infection of the kidneys.

Preventive measures may reduce symptoms and prevent recurrence of infection. Keeping the genital area clean and remembering to wipe from front to back may reduce the chance of introducing bacteria from the rectal area to the urethra.

Urinating immediately after sexual intercourse may help eliminate any bacteria that may have been introduced during intercourse. Refraining from urinating for long period of time may allow bacteria time to multiply, so frequent urination may reduce the risk of cystitis in those who are prone to urinary tract infections.

Increasing the intake of fluids (64 to 128 ounces per day) encourages frequent urination that flushes bacteria from the bladder. Drinking cranberry juice prevents certain types of bacteria from attaching to the wall of the bladder and may lessen the chance of infection.

Johns Hopkins patient information

Last revised: December 5, 2012
by David A. Scott, M.D.

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