Acute Pyelonephritis

Acute pyelonephritis is a bacterial infection of the renal parenchyma and renal pelvis, usually resulting from ascending infection from the lower urinary tract. It represents a severe form of urinary tract infection (UTI) and may lead to sepsis, renal abscess, or permanent renal damage if not promptly treated.

Outpatient therapy is appropriate only for clinically stable women of reproductive age without danger signs. All other patients require referral or hospital admission for parenteral therapy and monitoring.

Risk Factors

Patient-Related Factors

• Female sex

• Pregnancy

• Diabetes mellitus

• Immunosuppression

• Advanced age

• Previous urinary tract infection

Structural and Functional Factors

• Urinary tract obstruction

• Urolithiasis

• Vesicoureteral reflux

• Neurogenic bladder

• Benign prostatic hyperplasia (BPH)

Iatrogenic Factors

• Urinary catheterization

• Recent urological procedures

• Instrumentation of urinary tract

Causative Organisms

Most infections are caused by gram-negative bacteria:

• Escherichia coli (most common)

• Klebsiella species

• Proteus species

• Enterobacter species

• Pseudomonas aeruginosa (complicated infections)

Signs and Symptoms

Systemic Symptoms

• Fever (>38°C)

• Chills and rigors

• Malaise

• Nausea and vomiting

Local Symptoms

• Flank pain

• Costovertebral angle tenderness

• Abdominal discomfort

• Back pain

Lower Urinary Symptoms

• Dysuria

• Urinary frequency

• Urgency

• Haematuria

Severe disease may present with:

• Hypotension

• Confusion

• Septic shock

Diagnostic Criteria

Diagnosis is based on:

• Fever with flank pain or costovertebral tendernessAND

• Evidence of urinary infection

Supportive findings include:

• Pyuria

• Bacteriuria

• Positive urine culture

Danger Signs (Require Referral or Admission)

• Pregnancy

• Male patients

• Children or elderly patients

• Persistent vomiting

• Dehydration

• Sepsis or hypotension

• Altered mental status

• Renal impairment

• Urinary obstruction

• Immunocompromised state

• Failure of outpatient therapy

Investigations

Mandatory Tests

• Urinalysis (pyuria, bacteriuria, haematuria)

• Urine culture and sensitivity

• Full blood count

• Serum creatinine and urea

Additional Investigations

• Blood cultures (febrile patients)

• Electrolytes

• C-reactive protein (CRP)

Imaging (Indicated When)

• Poor clinical response after 48–72 hours

• Suspected obstruction

• Recurrent infection

• Severe illness

Imaging options:

• Renal ultrasound

• CT scan abdomen/pelvis (preferred in complications)

Management

Management depends on severity and patient risk category.

Pharmacological Management

1. Outpatient Treatment

(Stable non-pregnant women without danger signs)

Empirical therapy:

• Ciprofloxacin 500 mg orally every 12 hours for 7–14 days

OR

• Cefixime 400 mg orally once daily for 10–14 days

Adjust antibiotics according to culture results.

2. Inpatient Treatment

Indications:

• Complicated infection

• Severe systemic illness

• Inability to tolerate oral medication

Initial Parenteral Therapy

• Ceftriaxone 1–2 g IV once daily

OR

• Ciprofloxacin 400 mg IV every 12 hours

OR

• Gentamicin 5–7 mg/kg IV daily (where appropriate)

Switch to oral antibiotics once clinical improvement occurs.

Total treatment duration:10–14 days

Supportive Treatment

• Antipyretics (Paracetamol)

• Analgesics

• Antiemetics

• IV fluids for dehydration

Non-Pharmacological Management

• Adequate hydration

• Bed rest during acute illness

• Monitor urine output

• Early mobilization after improvement

• Removal or replacement of infected catheter if present

Management of Underlying Cause

• Relief of urinary obstruction

• Treatment of stones

• Management of prostate enlargement

Emergency decompression may be required via:

• Ureteric stenting

• Percutaneous nephrostomy

Referral Criteria

Immediate referral required for:

• Suspected urosepsis

• Pregnancy

• Male patients

• Recurrent pyelonephritis

• Renal impairment

• Obstructive uropathy

• Failure to improve within 48–72 hours

• Suspected renal abscess

Complications

• Urosepsis

• Septic shock

• Renal abscess

• Chronic pyelonephritis

• Renal scarring

• Acute kidney injury

• Papillary necrosis

Prevention

Primary Prevention

• Adequate fluid intake

• Proper perineal hygiene

• Post-coital voiding

• Avoid unnecessary catheterization

Secondary Prevention

• Early treatment of lower UTIs

• Control diabetes mellitus

• Correction of urinary obstruction

• Regular follow-up in recurrent infections

Patient Education

Patients should be advised to:

• Complete prescribed antibiotics fully

• Increase fluid intake

• Seek care urgently if fever persists

• Return immediately if vomiting or worsening pain develops

• Avoid self-medication with antibiotics

Prognosis

With early treatment, prognosis is excellent. Delayed or inadequate treatment increases risk of renal damage and systemic sepsis, especially in high-risk populations.