A kidney infection (pyelonephritis) usually starts as a bladder infection that travels up to one or both kidneys. It is more serious than a simple urinary tract infection and needs prompt treatment.
What started as a mild urine infection becomes fever and pain in her side. Because she recognises the warning signs and gets treated the same day, it clears without hospital admission.
| Bladder infection (cystitis) | Kidney infection |
|---|---|
| Burning when passing urine | Same urinary symptoms, plus: |
| Needing to pass urine often and urgently | Pain in the side, back or groin |
| Cloudy or smelly urine | High temperature and shivering |
| Lower tummy pain | Feeling very unwell, nausea or vomiting |
| Usually no fever | Confusion in older adults |
Get urgent help for a high fever with shaking, vomiting so you cannot keep fluids or antibiotics down, confusion, very fast breathing or heartbeat, or if you are pregnant. These can be signs of sepsis.
Treatment
- Antibiotics prescribed by a health professional, usually for 7–14 days
- Pain relief such as paracetamol
- Plenty of fluids
- Hospital treatment with IV antibiotics if very unwell, pregnant or unable to keep tablets down
- Follow-up if infections keep coming back
Who is at higher risk?
- Women, because of a shorter urethra
- Pregnancy
- Diabetes
- Kidney stones or an enlarged prostate
- Urinary catheters
“But it is just a urine infection, so I will wait for it to pass.”
A simple bladder infection sometimes clears, but a kidney infection usually needs antibiotics promptly. Left untreated, it can cause sepsis or kidney damage.
Your next step: If you have fever with back or side pain and urinary symptoms, contact a health professional today.
Related: UTI in women · Sepsis signs
Sources: NICE guideline NG111, Pyelonephritis (acute): antimicrobial prescribing; NHS kidney infection guidance.
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