What Is a Kidney Infection?

A kidney infection, or pyelonephritis, is a serious medical condition that occurs when harmful bacteria enter and infect the kidneys. The infection typically starts in the bladder or urinary tract and spreads upwards to the kidneys. Kidney infections can cause significant discomfort and may lead to complications if not treated promptly.

The prevalence of kidney infections can depend on various factors such as age, biological sex, and overall health. However, kidney infections are generally more common in people with vaginas compared to people with penises. This is due to a shorter urethra (the duct that guides urine from the bladder out of the body), which makes it easier for bacteria to reach the kidneys.

Kidney Infection Symptoms 

Common indications of a kidney infection include:

  • Fever and chills
  • Nausea and vomiting
  • Generalized discomfort in the abdomen
  • Discomfort or throbbing in the lower back, either on one or both sides or in the groin area
  • Needing to urinate more than normal
  • Persistent urge to urinate, even shortly after doing so
  • Painful or burning sensation during urination
  • Presence of blood or pus (a thick white or yellow fluid) in the urine
  • Cloudy or foul-smelling urine
  • Diarrhea

In children under the age of 2 who have a kidney infection, their primary manifestation may be limited to a high fever.

Conversely, in adults over the age of 65 with a kidney infection, the conventional symptoms may not be present. Instead, older individuals may primarily experience cognitive difficulties, such as:

  • Hallucinations
  • Confusion
  • Incoherent or jumbled speech

Should you notice any of these symptoms, it is crucial to promptly reach out to your healthcare provider. If you are presently undergoing treatment for a urinary tract infection (UTI) but continue to experience any of these symptoms, it is equally important to consult your provider.

What Causes Kidney Infections? 

Kidney infections typically result from the invasion of bacteria or viruses into the kidneys. Researchers suggest that the majority of kidney infections start as a bladder infection that travels up to infect one or both kidneys. 

The urinary tract usually has defenses to stop infections from moving up to the upper urinary tract. Urination, for example, usually flushes out bacteria before it reaches the bladder. But sometimes the body's defense mechanisms fail, leading to a urinary tract infection. If left untreated, the bacteria may progress to infect the kidneys. 

Less frequently, bacteria or viruses from other parts of the body may be transported to the kidneys via the bloodstream, causing an infection.

Risk Factors

Several risk factors can increase the likelihood of developing a kidney infection. These include:

  • Lower urinary tract infections: This is the most common cause of kidney infections. UTIs typically start in the bladder (cystitis) or urethra (urethritis). 
  • Urinary tract obstructions: These include anything that obstructs or blocks the flow of urine, such as kidney stones, an enlarged prostate in men, or structural abnormalities in the urinary tract.
  • Weakened immune system: Conditions such as diabetes, HIV/AIDS, or certain immunosuppressant medications may increase your risk of developing a kidney infection.
  • Catheter use: A urinary catheter is a tube inserted through the urethra that helps urine exit the bladder into a collection bag. People who use urinary catheters, such as those with urinary incontinence or who are bedridden, have an increased risk of developing urinary tract and kidney infections.
  • Pregnancy: This is due to hormonal changes that may affect urinary tract function. A growing uterus can exert pressure on the urinary system.
  • Vesicoureteral reflux: This is an abnormal flow of urine from the bladder back into the ureters and potentially to the kidneys. 
  • Sexual activity: This can introduce bacteria into the urinary tract, increasing the risk of developing a kidney infection.

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It's important to note that these are general risk factors, and individual circumstances may vary. If you suspect you have a kidney infection or have concerns about your risk factors, it's recommended to consult a healthcare professional for a proper evaluation and guidance.


To diagnose a kidney infection (pyelonephritis), healthcare professionals typically employ a combination of methods to assess symptoms, conduct physical examinations, and perform diagnostic tests. 

The diagnostic process may involve the following:

  • Medical history and physical examination: Your healthcare provider will want to determine what risk factors you have, if any. They can also help narrow down any lifestyle factors that may be causing your symptoms.
  • Urinalysis collection: This checks for bacteria, white blood cells (indicating an immune response), and red blood cells.
  • Blood tests: This test helps to evaluate kidney function and assess for other markers of infection or inflammation.
  • Imaging studies: This includes a computed tomography (CT) scan, ultrasound, and magnetic resonance imaging (MRI). These tests can provide a detailed view of the kidneys and urinary tract.

In some cases, additional tests may be necessary to investigate specific conditions. For example, if urinary tract abnormalities or vesicoureteral reflux are suspected, a voiding cystourethrogram (VCUG) may be performed. This test involves injecting a contrast dye into the bladder and urethra and taking X-rays during urination.

Treatments for Kidney Infections

Antibiotics are typically the first-line treatment for a kidney infection. Even before receiving diagnostic test results, your healthcare provider may prescribe an antibiotic that targets the most common types of bacteria that cause kidney infections. It’s important to take the entire prescribed course of antibiotics, even if symptoms improve.

The most common antibiotics used to treat kidney infections include:

  • Penicillins, such as Moxatag (amoxicillin)
  • Cephalosporins, such as Rocephin (ceftriaxone) or Vantin (cefpodoxime)
  • Sulfonamides, such as Bactrim (sulfamethoxazole/trimethoprim)
  • Fluroquinolones, such as Cipro (ciprofloxacin) or Levaquin (levofloxacin)
  • Aminoglycosides, such as Garamycin (gentamicin), are used in rare cases due to the risk of it causes renal toxicity

Once the lab results are available, your healthcare provider may adjust the antibiotic treatment to a more specific one that effectively treats the identified infection.

Antibiotics for kidney infections can be administered orally (by mouth), intravenously (through a vein in the arm), or a combination of both.

In severe cases, if you are very sick, hospitalization or bed rest may be necessary. Fluids may be administered through an intravenous (IV) line to ensure hydration and proper management.

If an obstruction such as a kidney stone or an enlarged prostate is identified as the cause of the urinary tract blockage, a doctor (usually a urologist, or a medical doctor who specializes in the urinary system) may opt for surgical or other procedural interventions to address the problem.


To help prevent kidney infections you can take the following measures:

  • Maintain good hygiene: Practice proper personal hygiene—especially in the genital area—to prevent the spread of bacteria that may cause infections.
  • Stay hydrated: Drink enough liquids to promote regular urination. This helps flush out bacteria and prevents them from multiplying in the urinary tract.
  • Avoid holding in urine: Emptying your bladder regularly helps prevent the growth of bacteria.
  • Wipe properly: When using the toilet, always wipe from front to back after to prevent bacteria from the anal region from spreading to the urethra.
  • Avoid using irritating feminine products: Certain feminine hygiene products, such as douches and powders, can irritate the urethra and increase the risk of infection. 
  • Wear breathable underwear: Choose underwear made of breathable materials like cotton. This allows air circulation and helps keep the genital area dry, reducing the risk of bacterial growth.
  • Treat urinary tract infections promptly: Timely treatment can help prevent the infection from spreading to the kidneys.

It's important to consult with a healthcare professional for personalized advice, especially if you have a history of recurrent kidney infections or other medical conditions. They can provide specific recommendations based on your situation.


Kidney infections, if left untreated or if they become severe, can lead to complications. These complications may include:

  • Kidney scarring: These are also called renal scars and they increase your chances of chronic kidney disease.
  • Chronic kidney disease: This is a long-term condition where the kidneys are unable to properly filter waste and excess fluids from the blood.
  • High blood pressure: This is a condition where the force of blood against the walls of the arteries is consistently too high.
  • Sepsis: This is a life-threatening infection that spreads through the bloodstream.
  • Kidney failure: This is when the kidneys are no longer able to filter waste and excess fluids from the body.

By preventing kidney infections, you reduce the risk of these potential complications.

Living With Kidney Infections

Living with kidney infections can be challenging, but with proper treatment and lifestyle adjustments, it is possible to manage the condition and help prevent complications. It is important to follow your healthcare provider's prescribed treatment plan, which may include taking antibiotics, staying hydrated, and practicing good hygiene. 

Regular follow-up visits with your provider are crucial to monitor kidney function and address any concerns or complications that may arise.

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