Kidney infection

Definition

A kidney infection, medically known as pyelonephritis, is a bacterial infection involving the renal pelvis and kidney parenchyma. It is a serious form of urinary tract infection (UTI) that can lead to sepsis or permanent renal damage if not treated promptly.

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Epidemiology

• More common in females due to shorter urethra and proximity to the anus.

• Peak incidence in young adult women and in elderly populations.

• Men are more prone in the presence of structural urinary tract abnormalities.

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Causes

• Primary Pathogen: Escherichia coli (~70–90% of cases).

• Other bacteria: Klebsiella pneumoniae, Proteus mirabilis, Enterococcus faecalis, Pseudomonas aeruginosa.

• Rarely, hematogenous spread from distant infections (e.g., Staphylococcus aureus bacteremia).

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Risk Factors

• Female gender.

• Previous urinary tract infections.

• Urinary tract obstruction (stones, enlarged prostate).

• Vesicoureteral reflux (especially in children).

• Diabetes mellitus.

• Pregnancy.

• Immunosuppression.

• Use of urinary catheters or stents.

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Pathophysiology

Bacteria typically ascend from the bladder through the ureters into the kidney. Less commonly, organisms spread via the bloodstream. The infection triggers inflammation, edema, and sometimes abscess formation, potentially impairing kidney function.

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Clinical Presentation

Symptoms

• Fever and chills.

• Flank or back pain (costovertebral angle tenderness).

• Nausea and vomiting.

• Dysuria, urinary frequency, urgency (concurrent lower UTI symptoms).

• Malaise and fatigue.

Signs

• Temperature often >38°C.

• Tenderness over the affected kidney.

• Tachycardia.

• Hypotension in severe cases (possible sepsis).

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Diagnosis

Laboratory

• Urinalysis: Pyuria, bacteriuria, hematuria, positive leukocyte esterase, nitrites (if Gram-negative bacteria).

• Urine culture: Confirms pathogen and guides antibiotic selection.

• Blood tests: Elevated WBC count, CRP, ESR; blood cultures if sepsis suspected.

• Renal function tests: Serum creatinine, urea.

Imaging (indicated in severe, recurrent, or complicated cases)

• Ultrasound: Detects obstruction, abscess, hydronephrosis.

• CT scan (without contrast for stone suspicion, with contrast for structural evaluation): More sensitive for abscesses or emphysematous pyelonephritis.

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Management

1. General Principles

• Prompt initiation of empiric antibiotics, later adjusted based on culture results.

• Hospitalization for severe cases, pregnant patients, or those unable to tolerate oral medications.

• Adequate hydration to promote urine flow.

• Pain management.

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2. Pharmacological Treatment

Uncomplicated Pyelonephritis (Outpatient)

• Ciprofloxacin: 500 mg orally twice daily for 7 days (avoid in pregnancy).

• Levofloxacin: 750 mg orally once daily for 5 days.

• Trimethoprim-sulfamethoxazole: 160/800 mg orally twice daily for 14 days (if pathogen is susceptible).

Pregnancy-safe alternatives

• Amoxicillin-clavulanate: 875/125 mg orally twice daily for 10–14 days.

• Cefalexin: 500 mg orally every 6 hours for 10–14 days.

Complicated Pyelonephritis (Hospitalized)

• Ceftriaxone: 1–2 g IV once daily.

• Cefepime: 1–2 g IV every 8–12 hours.

• Piperacillin-tazobactam: 4.5 g IV every 6–8 hours.

• Meropenem: 1 g IV every 8 hours (for suspected resistant Gram-negatives).

• Switch to oral therapy when patient is afebrile and clinically improved, to complete 10–14 days total treatment.

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3. Supportive Measures

• Adequate oral or IV fluids to maintain hydration.

• Analgesics: Paracetamol 500–1000 mg orally every 6 hours as needed for pain or fever.

• Avoid NSAIDs in patients with impaired kidney function.

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4. Special Considerations

• Pregnancy: Hospitalize initially; use pregnancy-safe antibiotics.

• Diabetes: Monitor glucose closely; increased risk of emphysematous pyelonephritis.

• Catheter-associated: Remove or replace catheter during treatment.

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Complications

• Renal or perinephric abscess.

• Sepsis and septic shock.

• Chronic pyelonephritis and scarring.

• Hypertension.

• Renal failure (rare in healthy individuals).

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Prevention

• Adequate hydration (aim for urine output ≥2 L/day).

• Prompt treatment of lower UTIs.

• Address structural abnormalities or obstructions.

• For recurrent infections: low-dose prophylactic antibiotics in selected patients.

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Prognosis

• Most patients recover fully with prompt treatment.

• Delayed or inadequate therapy increases the risk of complications and kidney damage.