Acute Pyelitis

Acute pyelitis is infection of the renal pelvis and collecting system, in clinical practice indistinguishable from acute pyelonephritis (infection of the renal pelvis and parenchyma). It is an upper urinary tract infection.

• Organisms: Escherichia coli (about 70 to 80 percent), Klebsiella, Proteus mirabilis (stones), Enterococcus faecalis, Pseudomonas aeruginosa (catheters, instrumentation), Staphylococcus saprophyticus and Staphylococcus aureus (haematogenous).
• Women are affected more than men (pregnancy, short urethra, sexual activity, diabetes). In men, an underlying structural problem such as prostatic obstruction is usual.
• Complicating factors: obstruction (stones, tumour, benign prostatic enlargement), vesicoureteric reflux, pregnancy, diabetes mellitus, immunosuppression, catheters, renal transplant, polycystic kidney disease, recent instrumentation, multi resistant organisms, older age.
• Complications: sepsis and septic shock, renal or perinephric abscess, emphysematous pyelonephritis (diabetics), pyonephrosis (infected obstructed kidney, a urological emergency), acute kidney injury, papillary necrosis, renal scarring, preterm labour in pregnancy.

• Fever above 38 C, rigors, flank or loin pain, costovertebral angle tenderness, nausea, vomiting, malaise, often with preceding dysuria, frequency and urgency. Older adults may present with confusion or falls and few urinary symptoms.
• Assess sepsis: tachycardia, hypotension, tachypnoea, raised lactate, altered mentation, oliguria.
• Red flags: hypotension, rigors with confusion, pregnancy, immunosuppression, solitary or transplanted kidney, known stones or obstruction, diabetes, persistent fever beyond 72 hours, severe colicky pain with haematuria (obstructing stone), anuria, male sex, recent catheter or instrumentation.
• Differentials: lower urinary tract infection, renal colic, pelvic inflammatory disease, appendicitis, diverticulitis, pneumonia (basal), cholecystitis, pancreatitis, herpes zoster, musculoskeletal pain, renal infarct.

• Urine dipstick (nitrites, leucocyte esterase, blood), microscopy and culture with sensitivity before antibiotics (colony count 10^4 CFU/mL or more).
• Bloods: full blood count (neutrophilia), CRP, urea and creatinine, electrolytes, glucose, blood cultures (positive in 20 to 30 percent), lactate if septic; pregnancy test in women of reproductive age.
• Imaging: renal tract ultrasound urgently for suspected obstruction, in men, in pregnancy, in the presence of known stones or renal impairment, or when there is no improvement within 48 to 72 hours; CT of the kidneys, ureters and bladder (non-contrast for stones, contrast enhanced for abscess or emphysematous change) if complicated or not improving.
• Outpatient eligible criteria: haemodynamically stable, no sepsis, able to take oral antibiotics, non-pregnant, no obstruction, reliable follow up.

• Admit if: sepsis, vomiting, unable to take oral treatment, pregnancy, obstruction or stones, solitary kidney or transplant, immunosuppression, diabetes with poor control, elderly frail, failed outpatient therapy, male with systemic illness.
• Oral outpatient therapy (non-pregnant adults, culture sent before first dose; adjust by culture and local resistance):
  • Ciprofloxacin 500 mg orally twice daily for 7 days (if local fluoroquinolone resistance is below 10 percent; avoid in tendon disease, epilepsy, aortic aneurysm, QT prolongation, pregnancy).
  • Co-amoxiclav 500/125 mg orally three times daily for 10 to 14 days (if the isolate is susceptible).
  • Cefalexin 500 mg orally three times daily (or 1 g twice daily) for 10 to 14 days.
  • Trimethoprim-sulfamethoxazole 160/800 mg orally twice daily for 14 days (only if the isolate is known to be susceptible).
  • Do not use nitrofurantoin or fosfomycin for pyelonephritis because renal tissue levels are inadequate.
  • A single dose of ceftriaxone 1 g intramuscularly or intravenously before oral therapy is reasonable if susceptibility is unknown.
• Intravenous therapy (hospital):
  • Ceftriaxone 1 to 2 g intravenously once daily; or cefuroxime 1.5 g intravenously every 8 hours; or co-amoxiclav 1.2 g intravenously every 8 hours; or gentamicin 5 mg/kg intravenously once daily (adjust to renal function and monitor levels; avoid prolonged use and in pregnancy and renal impairment).
  • Septic shock or resistant organisms: piperacillin tazobactam 4.5 g intravenously every 6 to 8 hours or meropenem 1 g intravenously every 8 hours (extended spectrum beta lactamase producers), with or without an aminoglycoside.
  • Switch to oral antibiotics according to culture after 24 to 48 hours of fever settling; total course 7 to 14 days depending on agent.
• Supportive: intravenous crystalloid for sepsis (30 mL/kg within the first 3 hours in septic hypotension), antipyretic and analgesia (paracetamol 1 g every 6 hours; NSAIDs avoided in acute kidney injury or dehydration; opioid if severe), antiemetic (ondansetron 4 mg intravenously or orally every 8 hours), adequate fluids, monitor urine output.
• Pregnancy: admit, intravenous ceftriaxone 1 to 2 g daily or cefuroxime 750 mg to 1.5 g intravenously every 8 hours; switch to oral cefalexin 500 mg three times daily when afebrile for 24 to 48 hours to complete 10 to 14 days; then prophylaxis with cefalexin 250 mg at night or nitrofurantoin 50 to 100 mg at night until delivery plus 2 weeks, and monthly cultures.
• Obstruction with infection: urgent decompression (percutaneous nephrostomy or retrograde ureteric stent) by urology or interventional radiology. Do not delay drainage.
• Reassess at 48 to 72 hours; if fever persists, repeat imaging for abscess, obstruction or resistant organism and modify antibiotics.
• Test of cure culture 1 to 2 weeks after completing therapy in pregnancy and recurrent or complicated infection; further investigation (ultrasound, cystoscopy) in men, in recurrent episodes and after a first episode with complicating factors.