Kidney Infection
A urinary tract infection that has reached the kidneys
Quick Facts
- Type: Urinary tract infection (upper)
- Main cause: Bacteria spreading from the bladder
- Key symptoms: Fever, chills, back or side pain
- Treatment: Prompt antibiotics
Overview
A kidney infection, known medically as pyelonephritis, is a urinary tract infection that has spread upward from the bladder to one or both kidneys. It is a more serious form of urinary tract infection because the kidneys are vital organs and infection there can cause significant illness.
Most kidney infections are caused by bacteria that travel up the urinary tract. With prompt antibiotic treatment, the great majority of people recover fully. However, if it is left untreated, a kidney infection can lead to kidney damage or allow bacteria to spread into the bloodstream, a dangerous condition called sepsis. For this reason, a suspected kidney infection should be assessed by a doctor promptly.
Symptoms
Symptoms of a kidney infection often develop quickly, over a few hours to a day, and tend to be more severe than those of a simple bladder infection.
- Pain in the back, side, or groin (often over one kidney)
- High temperature, chills, and shivering
- Feeling sick or vomiting
- Needing to urinate often, with pain or burning
- Cloudy, bloody, or strong-smelling urine
- Feeling generally unwell, weak, or exhausted
In older adults the picture can be less obvious, sometimes appearing mainly as confusion, weakness, or feeling generally unwell rather than the classic symptoms.
Causes
Kidney infections are almost always caused by bacteria, most commonly E. coli, which normally live in the bowel. The usual route is:
- Spread from the bladder: bacteria enter the urethra, multiply in the bladder, and travel up the ureters to the kidneys.
- Less commonly through the blood: bacteria from elsewhere in the body reach the kidneys via the bloodstream.
Anything that blocks the normal flow of urine or makes it easier for bacteria to ascend, such as a kidney stone, an enlarged prostate, or a urinary catheter, increases the risk.
Risk Factors
- Female sex, because of a shorter urethra
- A recent or recurrent bladder infection
- Urinary blockage from kidney stones or an enlarged prostate
- Pregnancy
- A urinary catheter
- Diabetes or a weakened immune system
- Conditions that prevent the bladder from emptying fully
Diagnosis
Doctors diagnose a kidney infection from the symptoms, examination, and tests on the urine and sometimes the blood.
- Urine test: a sample is checked for signs of infection and sent to identify the bacteria and the antibiotics that will work best.
- Blood tests: to look for markers of infection and assess kidney function.
- Examination: including checking for tenderness over the kidney area.
- Imaging: an ultrasound or CT scan may be done if the infection is severe, recurrent, or not improving, to look for stones or blockages.
Treatment
Kidney infections need prompt treatment with antibiotics, and most people improve within a few days of starting them.
- Antibiotics: usually taken by mouth for a course of one to two weeks; it is important to finish the whole course.
- Fluids: drinking plenty of fluids helps flush the urinary system.
- Pain and fever relief: such as paracetamol.
- Hospital treatment: needed for severe infections, for people who are very unwell, pregnant, vomiting, or unable to keep fluids down, where antibiotics and fluids may be given through a vein.
- Treating the cause: such as removing a stone or relieving a blockage if one is found.
If symptoms do not start to improve within about 24 to 48 hours of antibiotics, it is important to seek further medical review.
Prevention
Steps that lower the risk of urinary and kidney infections include:
- Drink plenty of fluids, mainly water, throughout the day
- Do not delay urinating when you need to, and empty the bladder fully
- Wipe from front to back after using the toilet
- Urinate after sexual intercourse
- Treat bladder infections promptly so they do not spread upward
- Manage conditions such as diabetes and kidney stones that raise the risk
When to See a Doctor
See a doctor promptly if you have urinary symptoms together with a fever, chills, or pain in your back or side, as these suggest a kidney infection that needs treatment. Seek emergency care if you or someone else has:
- A very high or persistent fever with shaking chills
- Severe back, side, or abdominal pain
- Repeated vomiting and inability to keep down fluids or medicines
- Confusion, drowsiness, or feeling extremely unwell
- A fast heartbeat, rapid breathing, or signs of sepsis
Pregnant women with suspected kidney infection should always be assessed urgently.
Frequently Asked Questions
How is a kidney infection different from a bladder infection?
A bladder infection (cystitis) affects the lower urinary tract and usually causes burning and frequent urination without fever. A kidney infection means bacteria have reached the kidneys and tends to cause fever, chills, and back or side pain, making it more serious and needing prompt treatment.
Is a kidney infection an emergency?
It can be. Many cases are treated with antibiotics at home, but a kidney infection can become serious if bacteria spread to the bloodstream. Seek emergency care for high fever with shaking chills, severe pain, repeated vomiting, confusion, or feeling extremely unwell.
How long does it take to recover from a kidney infection?
With the right antibiotics, most people start to feel better within a few days, though the full course usually lasts one to two weeks. It is important to finish all the antibiotics and to seek review if you are not improving after a day or two.
Can a kidney infection cause permanent damage?
Treated promptly, most kidney infections cause no lasting harm. If left untreated or if infections recur, there is a risk of kidney scarring or, rarely, reduced kidney function. This is why early treatment is important.
Why do women get kidney infections more often than men?
Women have a shorter urethra, so bacteria can reach the bladder and then the kidneys more easily. Pregnancy and sexual activity can further raise the risk. Simple measures such as good fluid intake and prompt treatment of bladder infections help reduce it.
References
- National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK).
- Mayo Clinic. Kidney infection (pyelonephritis).
- Centers for Disease Control and Prevention (CDC). Urinary tract infection.
- MedlinePlus, U.S. National Library of Medicine. Kidney infection.