Pyelonephritis is a serious bacterial infection of the kidney that can be acute or chronic.


One of the most common renal diseases, acute pyelonephritis is a sudden inflammation caused by bacteria. It primarily affects the interstitial area and the renal pelvis or, less often, the renal tubules.

Chronic pyelonephritis is persistent kidney inflammation that can scar the kidneys and may lead to chronic renal failure. This disease is most common in patients who are predisposed to recurrent acute pyelonephritis, such as those with urinary obstructions or vesicoureteral reflux.


Doctors believe that the bacterial infection causing pyelonephritis may sometimes develop elsewhere in the body and travel through the bloodstream to the kidney. Far more commonly, however, the infection is the result of bacteria from outside the body traveling back up the urinary stream through the urethra to the bladder and eventually to the kidneys, in which case it is known as an ascending infection. This may explain why women, whose urethras are short and in close proximity to the anus, a potential source of bacteria, have four times as many cases of pyelonephritis as men.

The flow of urine backward is known as reflux and may be caused by an anatomical defect or by an obstruction. In the former case, instead of a tight valve between the bladder and the ureter, there is a wide opening. When the bladder contracts during urination, the urine goes both ways, out through the urethra and back up through the ureters. The defect is not easy to correct and those who have it are subject to repeat infections.

Obstructions that cause reflux in women are commonly in the form of a stricture, or scar tissue, itself formed from infection or inflammation in the urethra. In young men, such strictures form less often and usually are a consequence of a sexually transmitted infection. In older men, the prostate is commonly responsible for obstruction to the flow of urine.

Reflux can also be caused by the insertion of catheters or instruments such as cystoscopes for diagnosis or treatment. The introduction of any foreign body into an area of obstruction is fraught with danger of infection which can be more difficult to treat.


No matter what the underlying cause, the symptoms of acute bacterial pyelonephritis are often the same. The first indications are usually shaking chills, accompanied by a high fever and pain in the joints and muscles including flank pain. Attention may not be drawn to the kidneys at all.

The situation may be especially confusing in children, when high temperature may suddenly bring on a seizure or a change in mental state, or in the aged, where fever may bring confusion, or the infection may be masked by generalized aches and pains.

There may be irritative voiding symptoms (burning when urinating, a sense of urgency, or increased frequency of urination).

In acute infections, the symptoms develop rapidly, the fever noted first, followed by possible changes in the color of the urine, and then tenderness in the flank. As the kidney becomes more inflamed, pain, loss of appetite, headache, and all the general effects of infection develop. This type of kidney pain differs from renal colic pain of kidney stones in that it is continuous and does not come in waves, stays in one spot, and may be worse by moving around.

While patients with chronic pyelonephritis may have acute infections, sometimes there are no symptoms, or the symptoms may be so mild that they go unnoticed. This carries the risk that the infectious inflammatory disease may progress slowly undetected over many years until there is enough deterioration to produce kidney failure. Thus, hypertension (high blood pressure) or anemia or symptoms related to renal insufficiency may be the first indication of trouble. Unfortunately, irreversible damage may have already taken place.


Your physician will take a medical history, perform a physical exam, and recommend tests including blood tests and blood cultures, urinalysis and urine culture, and possibly an ultrasound study of the kidneys.


Treatment centers on antibiotic therapy appropriate to the specific infecting organism, after identification by urine culture. When the infecting organism cannot be identified, therapy usually consists of a broad-spectrum antibiotic. Symptoms may disappear after several days of antibiotic therapy. Although urine usually becomes sterile within 48 to 72 hours, the course of such therapy is 21 days.

Patients with severe infections or complicating factors require hospitalization at least initially. In some patients, surgery may be necessary to relieve obstruction or correct an anatomical anomaly.

Follow-up treatment includes reculturing the urine several weeks after drug therapy stops in order to rule-out reinfection.

Patients at high risk of recurring urinary tract and kidney infections - such as those with prolonged use of an indwelling (Foley) catheter- require long-term follow-up.


Some cases of pyelonephritis can be prevented by prompt recognition and treatment of minor bladder infections that, if left untreated, may progress to this more severe condition.