ConditionKidneys & urinary tract
Kidney Infection (Pyelonephritis)
A kidney infection, or pyelonephritis, is a bacterial infection of one or both kidneys, usually caused by a bladder infection that travels upward. It causes fever, chills, pain in the back or side below the ribs, nausea or vomiting, and often burning or frequent urination. It is more serious than a bladder infection and needs prompt antibiotics, usually for 7 to 14 days. Most people feel better within 2 to 3 days of treatment. Untreated, it can lead to sepsis or kidney damage.
Also called: Pyelonephritis, acute pyelonephritis, renal infection, upper urinary tract infection, upper UTI
At a glance
- What it is
- A bacterial infection of the kidney, usually ascending from the bladder.
- Most common cause
- E. coli from the bowel.
- Key symptoms
- Fever, chills, flank or back pain, nausea, vomiting, plus urinary symptoms.
- Diagnosis
- Urine test and culture, blood tests; imaging if severe or not improving.
- Treatment
- Antibiotics for 7 to 14 days; hospital IV antibiotics if very unwell, pregnant or vomiting.
- Recovery
- Most improve within 48 to 72 hours of starting antibiotics.
When to get help
Call 911 or go to the ER
- Confusion, extreme drowsiness, very fast breathing, cold, clammy or mottled skin, or a racing heart (possible sepsis)
- Very low or no urine output
- Fever with severe flank pain and vomiting so you cannot keep fluids or tablets down
See a doctor within a day or two
- Fever above 38 °C (100.4 °F) with back or side pain and burning or frequent urination
- Any urinary infection symptoms in pregnancy, or with diabetes, a kidney transplant, a catheter or a weak immune system
- Symptoms not improving after 48 to 72 hours of antibiotics
- Kidney infection symptoms in a man or a child
Book a routine appointment
- Repeated kidney or bladder infections
Usually safe to manage at home
- Rest, fluids and pain relief alongside prescribed antibiotics once improving
How a kidney infection develops
Most kidney infections start as a urinary tract infection in the bladder. Bacteria from the bowel, usually E. coli, enter the urethra, multiply in the bladder, then travel up the ureters to the kidneys. Rarely, bacteria reach the kidney through the bloodstream.
Symptoms
Kidney infection symptoms
- fever, often 38.5 °C (101.3 °F) or higher, with shaking chills
- pain in the back, side (flank) or groin, usually on one side, below the ribs
- nausea and vomiting
- feeling very unwell and tired
- tenderness when the area over the kidney is tapped
Bladder symptoms that often come with it
- burning or pain when urinating
- needing to urinate often and urgently
- cloudy, smelly or bloody urine
- lower abdominal pain
Older adults may have few typical symptoms and instead become confused, fall or lose their appetite. Young children may have only fever, vomiting, irritability or poor feeding.
Kidney infection vs bladder infection
| Bladder infection (cystitis) | Kidney infection | |
|---|---|---|
| Fever | Usually none or low | Common, often high |
| Pain | Lower belly, burning urination | Back or side, plus bladder symptoms |
| Feeling unwell | Mild | Often significant, with nausea or vomiting |
| Treatment | Short antibiotic course (3 to 5 days) | Longer course (7 to 14 days), sometimes IV |
Risk factors
- female anatomy (short urethra)
- sexual activity and new partners
- pregnancy
- blockage of urine flow: kidney stones, enlarged prostate, structural abnormalities
- vesicoureteral reflux in children
- urinary catheters
- diabetes and weakened immunity
- spinal cord injury or nerve problems affecting bladder emptying
Diagnosis
- Urine dipstick and microscopy: white cells, nitrites and bacteria.
- Urine culture: identifies the bacteria and the best antibiotic. Always recommended in suspected kidney infection.
- Blood tests: blood count, kidney function and inflammatory markers; blood cultures if very unwell.
- Imaging: ultrasound or CT if symptoms are severe, there is no improvement after 48 to 72 hours, a stone or blockage is suspected, or infections recur. Children with a first febrile UTI may also have a kidney ultrasound.
Treatment
Antibiotics
- Outpatient treatment for people who can keep fluids and tablets down and are not severely ill. Common choices include fluoroquinolones (such as ciprofloxacin) or trimethoprim-sulfamethoxazole when local resistance and culture allow, often for 7 to 14 days depending on the antibiotic. Sometimes a first dose of an injected antibiotic is given.
- Hospital treatment with IV antibiotics for severe illness, vomiting, pregnancy, signs of sepsis, blockage, or failure to improve.
- Treatment is adjusted once culture results are available.
Finish the full course even if you feel better.
Symptom relief
- Drink plenty of fluids.
- Rest.
- Take acetaminophen (paracetamol) for fever and pain at the label dose. Ask your doctor before taking NSAIDs, which can affect kidney function during infection.
- A heating pad on the back or side may ease pain.
Treating blockages
An infected, blocked kidney, for example behind a stone, is an emergency and needs drainage with a stent or a tube through the skin (nephrostomy).
Complications
- Sepsis: infection spreading into the blood
- kidney abscess
- kidney scarring and, with repeated infections, chronic kidney disease
- in pregnancy, preterm labor
- emphysematous pyelonephritis, a severe gas-forming infection, mainly in people with diabetes
Recovery
Fever and pain usually improve within 48 to 72 hours of starting effective antibiotics. Tiredness may last a week or two. A follow-up urine test may be advised in pregnancy or with recurrent infection.
Prevention
- drink enough fluids so you urinate regularly
- urinate soon after sex
- wipe from front to back
- avoid spermicides if you get frequent UTIs
- treat bladder infections promptly
- for recurrent infections, your doctor may discuss vaginal estrogen after menopause, preventive antibiotics, or other options
Frequently asked questions
What are the first signs of a kidney infection?
Early signs often include fever and chills, pain in the back or side below the ribs, nausea, and bladder symptoms such as burning or frequent urination. Feeling generally very unwell is common.
How do I know if a UTI has spread to my kidneys?
A UTI may have reached the kidneys if you develop fever, chills, back or side pain, nausea or vomiting along with urinary symptoms. See a doctor the same day, because kidney infections need prompt antibiotics.
Can a kidney infection go away on its own?
No. Kidney infections need antibiotic treatment. Without it, the infection can spread to the blood (sepsis) or damage the kidneys.
How long does a kidney infection last?
With antibiotics, most people start feeling better within 2 to 3 days. Treatment usually lasts 7 to 14 days. Full recovery of energy may take another week or two.
Where is kidney infection pain felt?
Pain is usually felt in the back or side, just below the ribs, on one or both sides. It can spread around to the lower abdomen or groin. Tapping over the kidney area often causes tenderness.
Sources
This guide was written from current patient and clinical guidance, including:
- IDSA/ESCMID: International Clinical Practice Guidelines for the Treatment of Acute Uncomplicated Cystitis and Pyelonephritis in Women
- NIDDK: Kidney infection (pyelonephritis)
- NHS: Kidney infection
- MedlinePlus: Pyelonephritis - adults
- American Academy of Family Physicians: Acute pyelonephritis: diagnosis and treatment
- American Urological Association (Urology Care Foundation): Urinary tract infections in adults