Kidney infection, also known as renal infection or pyelonephritis, is a common type of urinary tract infection (UTI).

Bacteria often begins in the bladder or the urethra (a tube which transports urine from the bladder outside the body) and spreads to one of the kidneys, infecting it.

What is a kidney infection?

Women are more commonly affected by kidney infection, as are pregnant mothers, children under 2 years of age, and individuals over 60.

Kidney infections affect an estimated 3-4 men in every 10,000, and 15-17 women in every 10,000.

There are two types of kidney infection:

  • Uncomplicated kidney infection– the patient is healthy and serious complications are highly unlikely
  • Complicated kidney infection– the patient is more likely to suffer complications, perhaps because of a pre-existing illness or condition

If kidney infection is not treated promptly, there is a risk of serious complications, including kidney damage and blood poisoning (sepsis).

They are usually treated with antibiotics. In many cases, patients with kidney infection are hospitalized.

Symptoms of kidney infection

When someone has a kidney infection, it normally develops quite fast – in a day or a few hours. Symptoms of a kidney infection include:

  • Diarrhea
  • Nausea
  • Uncontrollable shivering
  • Vomiting
  • Back pain
  • Pain in the groin
  • Pain in the side
  • Often symptoms are worse when the patient urinates

If there is also a corresponding bladder infection (cystitis or urethritis) the individual may experience:

  • Bloody urine
  • Cloudy urine
  • Dysuria – pain or difficult urination, often described as a burning or stinging sensation
  • Foul-smelling urine
  • Frequent urination
  • Inability to urinate fully
  • Pain in the lower abdomen

Causes of kidney infections

A kidney infection is caused by bacteria entering the urethra and reproducing in the bladder, infecting it. The infection then spreads into the kidneys. There are a number of ways in which the bacteria can achieve this:

  • Toilet hygiene– after going to the toilet and using toilet paper to wipe one’s anus, there may be contact with the genitals, resulting in an infection getting through and working its way up to the kidneys. The infection could also enter via the anus; bacteria can exist in the colon and eventually cause a kidney infection.
  • Female physiology– women are more vulnerable to bladder infections and ultimately kidney infections than men, because their urethra is shorter, making it easier for infections to reach parts of the urinary tract more quickly.
  • Urinary catheter– a urinary catheter is a tube that is inserted into the bladder through the urethra to drain out urine. Having a urinary catheter raises the risk of developing a urinary tract infection, including kidney infection.
  • Kidney stones– individuals with kidney stones have a higher risk of developing kidney infection. Kidney stones are the result of a build-up of dissolved minerals on the inner lining of the kidneys.
  • Enlarged prostate– males with an enlarged prostate have a higher risk of developing kidney infections.
  • Sexually active females– if sexual intercourse irritates the urethra there may be a higher risk of bacteria getting inside the urinary tract and eventually reaching the kidneys.
  • Weakened immune systems– some patients with weakened immune systems may have a bacterial or fungal infection on their skin, which eventually gets into the bloodstream and attacks the kidneys.

What is the urinary tract?

The urinary tract consists of:

  • The kidneys– the majority of humans have two kidneys, one on either side of the abdomen. Kidneys clear toxins (poisons) from blood.
  • The ureters– urine passes from the kidneys to the bladder through tubes called ureters. Each kidney has one ureter connecting it to the bladder.
  • The bladder– a hollow organ (sac) in the lower abdomen that stores urine.
  • The urethra– a tube that carries urine from the bladder to outside the body. In males, the urethra travels down the middle of the penis to an opening at the end. In females, the urethra runs from the bladder to just above the vaginal opening. The urethra in females is shorter than in males.

Diagnosis of kidney infection

A doctor will usually check the patient’s heart rate, blood pressure, temperature, and respiratory rate to check their general state of health. The doctor will also check for signs of dehydration.

A physical exam will be carried out, with particular emphasis on the mid and lower back to see whether there is any sensitivity, pain, or tenderness.

If the patient is a young woman, the doctor may carry out a pelvic exam to verify whether there is any pelvic inflammatory disease (PID). If the female is of childbearing age, a pregnancy test may be recommended.

Urine test – this can determine whether there is a urinary tract infection, but not exactly where within the urinary tract (urethra, bladder, or kidneys). However, a urine test that detects an infection, plus other signs, such as pains (especially in the side of the body), will help the doctor reach a diagnosis.

Treatments for kidney infection

Kidney infection can either be treated at home or in a hospital; this will depend on several factors, including the severity of symptoms and the patient’s general state of health.

Treatment at home consists of taking prescribed oral antibiotics. The patient should start to feel better after a few days.

It is essential that the individual finishes treatment and complies with their doctor’s instructions.

Consuming plenty of fluids will help prevent fever and dehydration. Fluid intake recommendations may vary, depending on the type of infection.

The doctor may also prescribe an analgesic if there is any pain.

If the individual is treated in hospital and suffers from dehydration, fluids may be administered with a drip. Most cases of hospitalization do not last more than 3-7 days.

Subsequent urine and blood tests will tell the doctor how effective treatment has been.

The following types of patients are more likely to be treated in hospital for kidney infection:

  • Those withdiabetes
  • People aged 60 or over
  • Individuals who have serious difficulties urinating
  • Patients withcancer and those receiving chemotherapy or radiation therapy
  • Those with sickle cellanemia
  • Individuals with a history of kidney infection
  • People withHIV
  • Patients who are found to have a blockage in their kidneys
  • Pregnant women
  • Patients in severe pain
  • People with severe vomiting

Complications of kidney infection

  • EPN (emphysematous pyelonephritis)– this is a very rare complication; however, it is potentially fatal. EPN is a severe infection in which kidney tissues are destroyed rapidly. The bacteria that cause the infection release a toxic gas that accumulates inside the kidney, causing fever, nausea, abdominal pain, vomiting, and confusion.
  • Kidney abscesses– pus accumulates inside kidney tissues in small pockets (abscesses). Symptoms include blood in urine, weight loss, and abdominal pain. Sometimes surgery is needed to drain out the pus.
  • Sepsis (blood poisoning)– also a rare but possibly life-threatening complication. Bacteria spreads from the kidneys into the bloodstream, resulting in possible subsequent infections in any part of the body, including major organs. Symptoms include hypotension (low blood pressure), confusion, disorientation, diarrhea, weaker urine flow, clammy skin, cold skin, pale skin, and loss of consciousness. It is a medical emergency and patients are usually placed in an ICU (intensive care unit).

Preventing kidney infection

Often, a kidney infection is the result of a pre-existing infection in the urinary tract. The best way to prevent a kidney infection from developing is by not having bacteria in the urethra or bladder.

  • Hydration– drink plenty of fluids.
  • Urination– urinate whenever there is an urge. Don’t wait.
  • Sexual intercourse– urinate after sexual intercourse. Wash the genitals before and after intercourse.
  • Toilet hygiene– after defecating (passing stools) wipe the anus from front to back. This lessens the risk of spreading bacteria to the genitals.
  • Fiber– eat plenty of fiber so that stools come out easily and do not irritate or cause skin lesions. Constipation increases the risk of developing a urinary tract infection.


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