kidney with fever

Overview

A kidney infection, also called pyelonephritis (pie-low-nef-RYE-tis), is a type of urinary tract infection that affects one or both kidneys. It usually starts as a bladder infection and spreads upward. Fever is a common sign that the infection has reached the kidneys.

Kidney infections are less common than bladder infections, but they affect many people each year. They are one of the most common serious infections treated in hospitals.

Anyone can get a kidney infection, but they are more common in women, especially those who are sexually active, pregnant, or have a history of UTIs. People with diabetes, a weakened immune system, or urinary tract blockages are also at higher risk.

Symptoms

Common symptoms

• High fever (over 38°C)
• Pain in the back or side (flank pain)
• Chills and shivering
• Nausea or vomiting
• Pain or burning when urinating
• Frequent urge to urinate
• Cloudy, dark, or bloody urine

Symptoms in children

• Fever (often high)
• Vomiting
• Irritability or fussiness
• Poor feeding
• Abdominal pain
• Foul-smelling urine

Symptoms in older adults

• Confusion or change in mental state
• Fever
• Loss of appetite
• Weakness or fatigue
• Lower back pain
• Incontinence

Causes

Main causes

• A bacterial infection, most often from Escherichia coli (E. coli) bacteria that live in the bowel.
• The bacteria enter the urinary tract through the urethra and travel up to the bladder, then to the kidneys.
• Sometimes bacteria from other parts of the body can spread to the kidneys through the bloodstream.

Risk factors

• Being female (shorter urethra makes it easier for bacteria to reach the bladder)
• Sexual activity
• Pregnancy
• Diabetes or weakened immune system
• Blockages in the urinary tract (like kidney stones or enlarged prostate)
• Using a catheter (a tube to drain urine from the bladder)
• Previous urinary tract infections

When to see a doctor

See a doctor urgently if:

• If you have a fever and pain in your back or side
• If you have fever and symptoms of a urinary tract infection (burning pain when urinating, frequent urination)
• If you are pregnant and have a fever with urinary symptoms
• If your child has a fever and is vomiting or seems very unwell

Book a routine appointment if:

• If you have mild urinary symptoms without fever, see your GP within a few days.
• If you have recurrent UTIs, make an appointment to discuss prevention.

Diagnosis

Your doctor will ask about your symptoms and medical history. They will check your temperature, feel your abdomen and back for tenderness. They will usually order a urine test to check for infection.

Tests that may be done

• Urine dipstick test (checks for signs of infection)
• Urine culture (grows bacteria to identify the type)
• Blood tests (to check kidney function and look for infection in the blood)
• Imaging tests like ultrasound or CT scan (if the doctor suspects a blockage or complication)

What to expect at your appointment

You may be asked to provide a urine sample. The doctor might press on your lower back to see if it hurts. The urine test results may take a couple of days if a culture is done. If you are very unwell, you may be admitted to hospital for treatment.

Treatment

Kidney infections are treated with antibiotics to kill the bacteria. Depending on how severe the infection is and whether you can keep fluids down, treatment may be at home or in hospital.

Self-care at home

• Drink plenty of water to help flush out bacteria.
• Get plenty of rest.
• Take over-the-counter pain relievers like paracetamol for fever and pain (ask your pharmacist which is safe for you).
• Use a hot water bottle wrapped in a towel on your back for pain relief.

Medical treatments

Doctors will prescribe antibiotics, often for 7 to 14 days. You will usually start feeling better within a day or two, but it is important to finish the entire course of antibiotics even if you feel better. If you are vomiting or have a severe infection, you may receive antibiotics through a drip in hospital. Sometimes you may need a repeat urine test after treatment to make sure the infection is gone.

When is surgery considered?

Surgery is rarely needed for a simple kidney infection. It may be considered if there is an underlying problem like a kidney stone that blocks urine flow or an abscess that needs to be drained. In those cases, a urologist will discuss the options with you.

Living with this condition

After a kidney infection, it can take a few weeks to fully recover. You may feel tired and weak. Take things slowly and gradually return to normal activities. Drink plenty of fluids and go to the bathroom as soon as you feel the urge to urinate.

Lifestyle tips

• Drink plenty of water every day to keep urine diluted and flush out bacteria.
• Urinate after sexual activity to help prevent UTIs.
• Wipe from front to back after using the toilet to avoid spreading bacteria.
• Wear cotton underwear and avoid tight-fitting pants.
• Empty your bladder completely when you urinate.
• Avoid using perfumed products in the genital area.

Diet and exercise

There is no specific diet for kidney infections, but eating a balanced diet helps your immune system. Avoid too much salt if you have kidney problems. Stay active as tolerated, but rest when you feel tired. If you have kidney disease, follow any dietary advice from your doctor or dietitian.

Mental health and emotional wellbeing

A kidney infection can be painful and worrying. It is normal to feel anxious about your health. If you feel overwhelmed, talk to your doctor or a counselor. Remember that with proper treatment, most people recover fully. If you are feeling very low or having thoughts of harming yourself, contact a crisis helpline immediately.

Prevention

Many kidney infections can be prevented by treating bladder infections early and following good hygiene habits. If you have frequent UTIs, your doctor can discuss preventive measures, such as low-dose antibiotics or lifestyle changes.

Vaccines

There is no vaccine for kidney infections, but vaccines for other infections (like flu and pneumonia) can help protect your overall health, especially if you have chronic kidney disease.

Screening programmes

There is no standard screening for kidney infections. If you are at high risk (e.g., pregnant, have recurrent UTIs, or have kidney stones), your doctor may monitor you more closely.

Complications

If left untreated

• Kidney damage (scarring of the kidneys)
• Sepsis (a life-threatening infection spreading through the blood)
• Kidney abscess (a pocket of pus in the kidney)
• Recurrent infections
• In pregnant women, premature birth or low birth weight

Long-term outlook

The outlook for kidney infections is very good with prompt treatment. Most people recover fully within a few weeks without long-term problems. If complications occur, they can be treated, but it is important to seek medical attention early. Taking the full course of antibiotics and following up with your doctor greatly reduces the risk of recurrence or damage.

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