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Pyelonephritis refers to the inflammation of the kidney, most often caused by a bacterial infection. Pyelonephritis occurs when a pathogen (microorganism causing disease) enters and grows in your urinary tract, which includes a pair of kidneys and ureters (tubes that carry urine from the kidneys to the bladder), a urinary bladder, and a urethra (a small tube that carries urine from bladder to outside of the body). The urinary system is responsible for cleaning and filtering blood and producing urine as a waste product. Most commonly, the bacteria may enter the urinary bladder and travel up to the kidneys, or less commonly, the bacteria can enter through the bloodstream. Infections of the kidney results in the appearance of the symptoms, which may include fever, chills, a burning sensation when you pee, increased frequency of urine, tummy discomfort, pain in the flanks, etc.

For better outcomes, diagnosis and treatment must be initiated earlier in the course of the disease. Antibiotics are used to treat the infection. Untreated infections can lead to complications like pus collection, kidney damage, or a life-threatening blood infection. It is preventable by following some lifestyle changes.


Usually, your body keeps the pathogens away from your urinary system, but sometimes they evade the defense mechanism and cause disease. They mostly infect the lower urinary tract, including the urinary bladder and urethra. However, they may travel up and infect the kidneys causing pyelonephritis. Sometimes, the infection begins as cystitis (urinary bladder infection) and later involves the kidneys as well.

The most common bacteria causing pyelonephritis is E. coli, with the lesser common organisms including staphylococcus, klebsiella, pseudomonas, viruses, and fungi. These pathogens can enter the body via three routes: the ascending spread through the urethra, blood, or the area around the anus. 


The annual prevalence of pyelonephritis in the USA is found to be 15-17 cases per 10,000 females and 3-4 cases per 10,000 males. it is particularly more common in females, but its incidence increases in males after the age of 55 years. 

Risk Factors

The following risk factors may increase your chances of getting pyelonephritis:

Gender: Women are more prone to cystitis and pyelonephritis than men because of the short distance between the anus and urethra. The use of certain contraceptives like diaphragm and spermicides also increases the risk and so does menopause. Decreased levels of estrogen hormone and vaginal atrophy after menopause may lead to decreased levels of protective organisms in the vagina, increasing the chances of urinary tract infections (UTI).   In older males, the prostate gland enlarges and obstructs the urine outflow which can increase their risk. The urinary bladder and urethra can also be co-infected with the prostate gland.

Sexual activity: Sexually active women are more prone to pyelonephritis.

Urinary catheters: You may have an increased risk of cystitis and pyelonephritis if a catheter is placed in your urinary tract due to immobility, recent surgery, or neurological disease. A urinary catheter is a flexible tube that is used to empty the bladder and collect urine in a urine bag.

Structural abnormalities in the Urinary tract: Sometimes there is a structural abnormality of the urinary tract which results in the accumulation of urine, resulting in recurrent infections. These may include extra valves, small kidneys, and tortuous course of ureters in children, while stones, constipation, and enlarged prostate are more common in adults.

Weakened immune system: A weak immune system due to diabetes or cancer medications (chemotherapy) can also increase the risk of the infection.

Pregnancy: The hormonal changes in pregnancy lead to certain changes in the urinary tract that may make you more prone to a UTI and pyelonephritis. Moreover, the pregnant uterus puts pressure on the bladder which hinders the complete emptying of the bladder, predisposing it to infection.

Other: Other risk factors may include recent urinary tract instrumentation, recent exposure to antibiotics, recurrent infections, and advanced age.

Family history: If you have a family history of recurrent UTIs, you may be at increased risk too. 

Signs And Symptoms

Symptoms of pyelonephritis appear rapidly over a few hours or a day. You may have the following signs and symptoms;

  • Fever
  • Chills
  • Nausea, vomiting
  • Flank, back pain
  • Burning sensation during pee (dysuria).
  • Increased frequency and urge to pee.
  • Urine that may be cloudy, bloody, or smelly.
  • Discomfort or pain in the lower abdomen.


If you feel having the symptoms of pyelonephritis, you should immediately contact your healthcare provider for prompt diagnosis and treatment. It should be started early for better outcomes and to prevent complications. Usually, a diagnosis of simple pyelonephritis is made based on signs and symptoms, and a few of the following tests;

Urinalysis: The doctor may ask you to submit a sample of clean urine, which will be checked in the lab for urinary nitrites, white blood cells (leukocytes), leukocyte esterase, and red blood cells.

Urine culture: This test may be ordered in unresolved cases. In this test, a causative organism is grown in the lab and its susceptibility to antibiotics is assessed. After this specific antibiotics would be started.

Imaging studies:  If the symptoms are not resolved with initial treatment or you are having recurrent UTIs, a doctor may advise imaging studies like X-ray KUB, Ultrasound, CT scan, or MRI of the abdomen and pelvis,  to check for structural abnormalities and stones.

Differential Diagnosis

Several other conditions may mimic the appearance of pyelonephritis;

·         Acute Abdomen and Pregnancy

·         Acute Bacterial Prostatitis

·         Appendicitis

·         Cervicitis

·         Chronic Bacterial Prostatitis

·         Cystitis

·         Endometritis

·         Pelvic Inflammatory Disease


People with pyelonephritis are started on empirical antibiotics until the results of their urinary culture have been obtained after which the initial atibiotics are replaced with antibiotics to which the infecting bacteria are found to be sensitive. Simple cases are treated as an out-patient with advice on improving hydration. Most of the bacteria are sensitive to fluoroquinolones (ciprofloxacin or levofloxacin), cephalosporins (ceftriaxone), aminoglycosides, or trimethoprim/sulfamethoxazole. These antibiotics are used alone or in combination.

Some cases acquire a severe course with very high fever and deteriorating condition. They need to be admitted to the hospital for intravenous antibiotics and hydration. The sensitive antibiotics are started and constant observation is maintained to prevent complications. 


With prompt diagnosis and proper treatment, the outcome is usally good. For complicated cases, further testing is done to find out the cause and treat it. 


  • Good personal hygiene: Cleaning the urogenital area from front to back, avoidance of using scented materials, frequently changing pads and tampons, and taking regular showers may decrease your chances of getting pyelonephritis.
  • Changing urination habits: Don’t hold the urine and use the toilet when you feel the need.  Douching is not recommended by healthcare professionals.
  • Hydration: Drink plenty of fluids, especially water, i.e., drinking 6-8 glasses of water per day is recommended. Avoid fluids that may irritate your bladder like caffeine, alcohol, citrus juices, etc.
  • Contraceptive methods: If you are using diaphragms, condoms, or spermicides you may need to ask your doctor about changing your birth control method.

Our clinical experts continually monitor the health and medical content posted on CURA4U, and we update our blogs and articles when new information becomes available. Last reviewed by Dr.Saad Zia on May 27, 2023.


Kidney Infection (Pyelonephritis): Symptoms, Diagnosis & Treatment - Urology Care Foundation (urologyhealth.org)


Cystitis and Pyelonephritis - Primary Care: Clinics in Office Practice (theclinics.com)


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