Kidney Infection

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What is a kidney infection?

A kidney infection is a type of urinary tract infection (UTI). Most people think of a UTI as a bladder infection. In fact, the bladder is just one part of the urinary tract. The other parts are the kidneys, ureters and urethra. Any part of the system can become infected. So, it really isn’t a matter of a kidney infection vs. UTI. A kidney infection is a form of UTI. The medical name for a kidney infection is pyelonephritis.

The kidneys sit at about the level of the bottom of the ribs on either side of the spine in the back. They are the body’s “filter” and clean the blood of waste products. They also play a vital role in water and electrolyte balance, blood pressure regulation, and red blood cell production. The end product of their work is urine, which flows down from them through the ureters and bladder then out of the body through the urethra.

In most cases, kidney infections occur when bacteria first infect the bladder and travel up the system to the kidneys. The infection can affect one or both kidneys. Most kidney infections are acute, meaning they develop rather rapidly over a brief period of time. Although uncommon, kidney infections can become chronic. In almost all cases, a chronic kidney infection is due to a major anatomic abnormality that increases the likelihood of infections or makes them more difficult to treat.

Kidney infection causes typical symptoms of a UTI, such as burning and frequent urination. However, a kidney infection is more serious than other UTIs. Additional symptoms that can indicate kidney involvement include back pain, fever, chills, nausea and vomiting. These symptoms can start suddenly.

Bacterial kidney infections require treatment with antibiotics and plenty of fluids. In some cases, hospitalization is necessary to safely and effectively treat a kidney infection. Doctors treat chronic kidney infections by correcting the anatomic abnormality if possible. Otherwise, long-term antibiotic treatment may be necessary. Kidney transplantation is a last resort.

A kidney infection requires immediate medical attention. Left untreated, it can cause kidney damage, which can be permanent, or a life-threatening infection if bacteria spread to the blood. Seek medical care right away if you have symptoms of a kidney infection or if you have a UTI that isn’t getting better with medicine.

What are the symptoms of a kidney infection?

Kidney infection symptoms can vary depending on your age.

Common symptoms of a kidney infection

The most common kidney infection symptoms include:

  • Burning, stinging or pain with urination
  • Cloudy, bloody or bad-smelling urine that may contain pus
  • Fever and chills
  • Frequent, persistent or urgent need to urinate or a feeling of needing to empty your bladder again right after urinating

In children under 2 years of age, a high fever may be the only symptom of a kidney infection. Older people over age 65 may not have either fever or common symptoms. Instead, they can have atypical symptoms, such as confusion, disorganized speech, and hallucinations.

Seek prompt medical care for symptoms of a kidney infection. It needs immediate treatment to prevent complications. You should also see your doctor promptly if you are being treated for a UTI, but it isn’t getting better.

Serious symptoms that might indicate a life-threatening condition

In some cases, a kidney infection can lead to life-threatening complications, including sepsis and dehydration. Seek immediate medical care (call 911) if you, or someone you are with, have any of these life-threatening symptoms including:

  • Confusion or disorientation
  • Low or no urine output

What causes a kidney infection?

Under normal circumstances, urine is sterile—there are no microorganisms in it. Most acute kidney infections occur when bacteria infect the bladder and travel up to the kidneys. Bacteria from the bowel are the most common culprits, especially Escherichia coli (E. coli). Bacteria are plentiful in the rectal area and can get inside the urethra. The body is usually able to wash them out with urine. Sometimes, they overcome the body’s defenses and cause a bladder infection. About 1 in 30 bladder infections will result in a kidney infection.

In some cases, a kidney infection is caused by bacteria or viruses from other parts of the body circulating through the blood to the kidneys.

Chronic kidney infections are almost always due to a major anatomic abnormality, such as structural problems with the ureters (ureters connect the kidneys to the bladder). The abnormality may obstruct the normal flow of urine through the urinary tract, making it easier for infections to take hold. Obstructions can also make it easier for kidney stones to form.

What are the risk factors for a kidney infection?

Several factors increase the risk of developing a kidney infection, including:

  • Being female. UTIs, including kidney infections, are more common in women than men. The female anatomy puts the urethra closer to sources of bacteria, including the vagina and anus. The female urethra is also shorter, making it easier for bacteria to reach the bladder.
  • Being pregnant. Pregnant women have an even higher risk of UTI. A kidney infection can be very serious during pregnancy.
  • Having a blockage or structural abnormality. These issues can cause urine to flow the wrong way, back up the urinary tract. They can also dramatically slow the flow of urine, which is one of the body’s natural defenses against infection.
  • Having diabetes or a weakened immune system. Both of these conditions make you more prone to developing infections.
  • Having nerve or spinal cord damage. This can limit your ability to sense symptoms of a bladder infection. Letting it go untreated can lead to a kidney infection.
  • Using a urinary catheter. Urinary catheters can act as “superhighways” for bacteria to enter the urinary tract.

Reducing your risk of a kidney infection

Preventing UTIs, including kidney infections, relies on maintaining a healthy urinary tract. You may be able to lower your risk of a kidney infection by:

  • Avoiding scented feminine products, such as deodorants or douches, which can be irritating and leave the urethra vulnerable to infection
  • Drinking plenty of fluids each day, with water being the best choice
  • Not holding urine for too long and urinating as soon as you feel the urge
  • Urinating as soon as possible after sexual activity and intercourse
  • Wiping from front to back to avoid introducing bacteria from the rectal area into the urethra

If you have a bladder infection, it’s important to pay attention to your symptoms once you start treatment. Symptoms that persist or worsen despite treatment are a red flag to see your doctor.

How is a kidney infection treated?

Antibiotics are the main kidney infection treatment because most cases are due to a bacterial infection. The antibiotic course will last at least a week and usually longer. It’s important to finish the entire course, even when you start to feel better. Most people will notice improvement after a few days. But your body needs the entire course to fully kill the infection. Skipping doses or stopping before the course is complete increases the risk of recurrence and resistance. If this happens, the infection can be harder to treat.

While you are treating a kidney infection, you should follow the same steps that can help prevent a urinary tract infection. In particular, you should make an effort to drink plenty of water. This helps flush out the bacteria from your system. Avoid beverages with caffeine or alcohol, which can be irritating to the urinary tract. These drinks can also contribute to dehydration.

In severe cases, a kidney infection may require hospitalization for IV (intravenous) antibiotics and fluids. If kidney infections are the result of blockages or structural problems, surgery may be necessary to treat recurrent or chronic infections. If surgery can’t fix the problem, long-term antibiotics or kidney transplantation are potential treatment options.

What are the potential complications of a kidney infection?

Complications from a kidney infection can be serious and even life threatening. The two main concerns are kidney damage, which can be permanent, and sepsis. A kidney infection can cause scarring in the kidney. This can lead to chronic kidney disease (CKD) and kidney failure.

Because the kidneys filter blood, an infection can spread from the kidneys to the blood. This can cause very serious and life-threatening problems. It can trigger sepsis, which is an extreme and overwhelming response to an infection. It results in widespread inflammation and can quickly lead to organ failure and death.

Pregnant women who develop a kidney infection can have pregnancy complications. It increases the risk of delivering a low birth weight baby.

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Medical Reviewer: William C. Lloyd III, MD, FACS
Last Review Date: 2020 Nov 4
THIS TOOL DOES NOT PROVIDE MEDICAL ADVICE. It is intended for informational purposes only. It is not a substitute for professional medical advice, diagnosis or treatment. Never ignore professional medical advice in seeking treatment because of something you have read on the site. If you think you may have a medical emergency, immediately call your doctor or dial 911.