Pyelonephritis

How pyelonephritis develops

Most cases start as a bladder infection (cystitis). Bacteria from the bowel colonize the urethra, multiply in the bladder, then ascend through the ureters to the kidney. Some E. coli strains carry special attachment hairs (P fimbriae) that help them climb. Less commonly, infection reaches the kidney through the bloodstream, as with Staphylococcus aureus.

Factors that let bacteria reach the kidney or stay there:

• Urine flow problems: kidney stones, an enlarged prostate, strictures, tumors, a neurogenic bladder, or hydronephrosis.
• Vesicoureteral reflux: urine flowing back from bladder to kidney, the main cause in young children.
• Pregnancy: hormones relax the ureters and the growing uterus compresses them.
• Diabetes and immunosuppression.
• Catheters, stents and recent urinary procedures.
• Female anatomy: a shorter urethra; sexual activity and spermicides raise bladder infection risk.

Types of pyelonephritis

Symptoms

Classic acute pyelonephritis:

• fever (often above 38.5 °C / 101.3 °F) and shaking chills
• pain in the flank (side and back below the ribs), usually one side
• tenderness when the area over the kidney is tapped (costovertebral angle tenderness)
• nausea and vomiting
• burning, frequency and urgency of urination, cloudy or bloody urine (not always present)

Variations:

• Older adults: may have confusion, falls or just feel unwell, without fever or pain.
• Infants and young children: fever, irritability, vomiting and poor feeding, without obvious urinary symptoms.
• Chronic pyelonephritis: often few symptoms; found through high blood pressure, protein in urine or reduced kidney function.

For a plain-English guide to recognizing and recovering from a kidney infection, see kidney infection.

How pyelonephritis is diagnosed

1. Urinalysis: white cells, nitrites and often blood. White cell casts point to kidney involvement.
2. Urine culture with sensitivities: should be sent in every case of suspected pyelonephritis to guide antibiotic choice, since resistance is rising.
3. Blood tests: blood count, kidney function and inflammatory markers. Blood cultures if very unwell or admitted.
4. Pregnancy test in women of childbearing age.
5. Imaging: not needed in most uncomplicated cases. It is recommended when: - symptoms do not improve after 48 to 72 hours - there is suspected obstruction, stone, abscess or gas - the patient is very ill or septic, or has diabetes, a single kidney or immunosuppression - the infection recurs quickly

CT of the abdomen and pelvis with contrast is the most informative test; ultrasound is used in pregnancy, children and to check for blockage.

1. Children: a kidney ultrasound after a first febrile UTI in infants, and sometimes a voiding cystourethrogram (VCUG) to look for reflux.

Pyelonephritis treatment

Outpatient treatment

Healthy adults who can take fluids and tablets are usually treated at home. Antibiotic choice depends on local resistance and the culture result:

• Fluoroquinolones (ciprofloxacin, levofloxacin): effective, short courses of 5 to 7 days, where resistance is low. They carry warnings about tendon, nerve and aortic side effects.
• Trimethoprim-sulfamethoxazole: 14 days, if the organism is known to be susceptible.
• Oral beta-lactams (such as cefpodoxime or amoxicillin-clavulanate): usually 10 to 14 days; less effective, often started after a single IV dose of ceftriaxone.

Nitrofurantoin and fosfomycin are good for bladder infections but do not reach adequate levels in the kidney and are not used for pyelonephritis.

Hospital treatment

Admission is needed for sepsis, persistent vomiting, pregnancy, obstruction, severe illness, or failure of oral therapy. IV options include ceftriaxone, piperacillin-tazobactam, carbapenems for resistant organisms, and aminoglycosides. Patients switch to tablets once fever settles and they can eat and drink.

Treating blockage

An infected, blocked kidney is a urological emergency. The kidney is drained with a ureteral stent or a nephrostomy tube through the back. Stones are treated once infection has cleared.

Supportive care

Fluids, rest, and acetaminophen (paracetamol) for fever and pain, following the label dose. Avoid NSAIDs if kidney function is reduced.

In pregnancy

Pyelonephritis in pregnancy is treated in the hospital with IV antibiotics (usually a cephalosporin), because it can trigger preterm labor and respiratory complications. Fluoroquinolones and tetracyclines are avoided. Many women are then given low-dose preventive antibiotics for the rest of pregnancy. Routine screening for bacteria in urine in early pregnancy aims to prevent it.

Complications

• sepsis and septic shock
• kidney or perinephric abscess
• acute kidney injury
• scarring, especially in young children, leading to high blood pressure and chronic kidney disease later
• emphysematous pyelonephritis in diabetes
• preterm birth in pregnancy

Preventing recurrence

• Treat bladder infections promptly.
• Drink enough fluid to pass pale urine, and do not delay urinating.
• Manage stones, prostate enlargement and reflux.
• For recurrent infections, options include vaginal estrogen after menopause, preventive antibiotics, and investigation for an underlying cause.

Frequently asked questions

What is the difference between pyelonephritis and a UTI?

Pyelonephritis is a type of urinary tract infection that involves the kidney (an upper UTI). Most UTIs are bladder infections (cystitis), causing burning and frequency without fever. Fever, chills, flank pain and vomiting suggest the infection has reached the kidney and needs stronger, longer antibiotic treatment.

What antibiotics treat pyelonephritis?

Common choices are a fluoroquinolone such as ciprofloxacin for 5 to 7 days, trimethoprim-sulfamethoxazole for 14 days if the bacteria are susceptible, or a cephalosporin, sometimes after an IV dose of ceftriaxone. Severe cases receive IV antibiotics. Nitrofurantoin is not suitable for kidney infections.

What is chronic pyelonephritis?

Chronic pyelonephritis is long-term inflammation and scarring of the kidney caused by repeated or persistent infection, usually linked to vesicoureteral reflux in childhood or long-standing blockage. It may cause few symptoms but can lead to high blood pressure, protein in the urine and chronic kidney disease.

When is a CT scan needed for pyelonephritis?

Imaging is not needed for most uncomplicated cases. A CT scan, or ultrasound in pregnancy and children, is recommended if there is no improvement after 48 to 72 hours, signs of sepsis, suspected stones or blockage, diabetes, a single kidney, or recurrent infection.

How long does it take to recover from pyelonephritis?

Most people feel better within 48 to 72 hours of starting effective antibiotics, with fever settling first. Tiredness can last a week or two. A repeat urine culture is usually only needed if symptoms persist or recur, or during pregnancy.