Acute Kidney Infection

Acute kidney infection (acute pyelonephritis) is bacterial infection of the renal parenchyma and collecting system, usually ascending from the bladder.

• Organisms: Escherichia coli (70 to 85 percent), Klebsiella, Proteus, Enterococcus, Pseudomonas, Staphylococcus saprophyticus; extended-spectrum beta-lactamase producers are increasingly common.
• Risk factors: female sex, pregnancy, diabetes, urinary stones, obstruction, vesicoureteric reflux, catheterisation, instrumentation, immunosuppression, HIV, spinal cord injury, neurogenic bladder, urinary schistosomiasis.
• It is a leading cause of sepsis in women and of hospital admission.

Fever, chills and rigors, flank or loin pain, costovertebral angle tenderness, nausea, vomiting, dysuria, frequency, urgency, malaise.

• Elderly, diabetic and immunosuppressed patients may present with confusion, falls or sepsis alone.
• Differential diagnosis: acute cystitis, renal colic with infection, appendicitis, pelvic inflammatory disease, cholecystitis, pneumonia (lower lobe), diverticulitis, epididymo-orchitis, renal abscess, herpes zoster, musculoskeletal pain, malaria.
• Complications: bacteraemia and septic shock, renal or perinephric abscess, emphysematous pyelonephritis (diabetes), pyonephrosis with obstruction, papillary necrosis, acute kidney injury, preterm labour in pregnancy, chronic pyelonephritis and scarring in children, xanthogranulomatous pyelonephritis.

Urinalysis (leucocyte esterase, nitrite, pyuria, white cell casts, haematuria) and midstream urine culture before antibiotics; blood cultures if febrile and septic.

• Full blood count, creatinine, electrolytes, C-reactive protein, glucose, lactate in sepsis; pregnancy test.
• Imaging (ultrasound, or contrast CT) for failure to improve within 48 to 72 hours, diabetes, suspected stone or obstruction, sepsis, recurrent infection, and male sex.
• Urine for schistosome ova in endemic areas.

Supportive: oral or intravenous fluids, antipyretics (paracetamol 1 g every 6 hours), analgesia, antiemetics.

Pharmacological (adjust to culture and local resistance):

• Outpatient, mild to moderate: ciprofloxacin 500 mg twice daily for 7 days (or levofloxacin 750 mg daily for 5 days), or cefixime 400 mg daily for 10 days, or amoxicillin-clavulanate 625 mg three times daily for 10 to 14 days, or cotrimoxazole 960 mg twice daily for 14 days if the isolate is susceptible.
• Parenteral for severe disease, vomiting, pregnancy or sepsis: ceftriaxone 1 to 2 g IV daily, or gentamicin 5 mg/kg IV daily (with amoxicillin 1 g every 8 hours) or amikacin 15 mg/kg daily; switch to oral when afebrile for 24 to 48 hours; total 7 to 14 days.
• Extended-spectrum beta-lactamase producers: meropenem 1 g IV every 8 hours or ertapenem 1 g IV daily.
• Pseudomonas: piperacillin-tazobactam 4.5 g IV every 6 hours or ceftazidime 2 g IV every 8 hours.
• Children: ceftriaxone 50 to 75 mg/kg IV daily; oral cefixime 8 mg/kg daily or cefalexin 25 mg/kg twice daily, for 7 to 10 days.
• Pregnancy: admit; ceftriaxone 1 g IV daily until afebrile for 48 hours, then oral cefalexin 500 mg four times daily to complete 10 to 14 days, followed by nitrofurantoin 100 mg at night until delivery; avoid fluoroquinolones, doxycycline, and cotrimoxazole in the first trimester.

Procedures: relieve obstruction urgently by ureteric stent or percutaneous nephrostomy; drain abscesses above 3 to 5 cm; nephrectomy for emphysematous or xanthogranulomatous disease unresponsive to drainage.

Special groups: diabetes (glucose control, imaging), men (prostatitis, 14 days of therapy), catheterised patients (change catheter), HIV.

Red flags: hypotension, rigors with obstruction, persistent fever beyond 72 hours, pregnancy, gas on imaging.

Follow-up: culture again only if symptoms persist; urine culture after therapy in pregnancy; ultrasound to look for structural disease after the first childhood or male episode.