What is pyelonephritis?

Pyelonephritis: Definition and Clinical Presentation

Pyelonephritis is defined as inflammation of the renal parenchyma due to bacterial infection, affecting the kidney and renal pelvis, typically presenting with fever, flank pain, and urinary symptoms. 1

Clinical Presentation

• Typical symptoms include fever (>38°C), chills, flank pain, nausea, vomiting, and tenderness at the costovertebral angle 2, 1
• Patients may also present with symptoms of lower urinary tract infection (frequency, urgency, dysuria) 1
• In some populations (particularly diabetics), up to 50% may not exhibit typical flank tenderness, making diagnosis more challenging 1
• Flank pain is nearly universal in pyelonephritis, and its absence should raise suspicion of an alternative diagnosis 3

Diagnostic Approach

• Urinalysis showing white blood cells, red blood cells, and nitrite is recommended for routine diagnosis 2, 1

• Urine culture with antimicrobial susceptibility testing should be performed in all cases of suspected pyelonephritis before initiating antibiotics 2, 1

• Evaluation of the upper urinary tract via ultrasound should be performed to rule out urinary tract obstruction or renal stone disease in patients with:

  • History of urolithiasis
  • Renal function disturbances
  • High urine pH 2

• Additional imaging (contrast-enhanced CT scan) should be considered if:

  • Patient remains febrile after 72 hours of treatment
  • There is deterioration in clinical status 2
  • No improvement in symptoms or recurrence after initial improvement 3

Types of Pyelonephritis

• Uncomplicated pyelonephritis: Infection limited to non-pregnant, premenopausal women with no known relevant urological abnormalities or comorbidities 2
• Complicated pyelonephritis: Presence of urinary obstruction, abscess, sepsis, renal insufficiency, solitary kidney, or significant comorbidity 4

Causative Organisms

• Escherichia coli is the most common pathogen, accounting for 70-90% of infections 5
• Other causative organisms include Enterococci, Klebsiella pneumoniae, Enterobacter cloacae, Serratia marcescens, Proteus mirabilis, Pseudomonas aeruginosa, and Staphylococci 6, 5
• There is a rising incidence of infections with bacteria that produce extended-spectrum beta-lactamase (ESBL) enzymes, which have developed resistance to many antibiotics 5

Treatment

Outpatient Management

• Outpatient treatment is appropriate for most patients with uncomplicated pyelonephritis who can tolerate oral therapy 7
• Fluoroquinolones (such as ciprofloxacin) are recommended for oral empiric treatment of uncomplicated pyelonephritis 2
• Ciprofloxacin is indicated for complicated urinary tract infections and pyelonephritis 6
• When local resistance to a chosen oral antibiotic likely exceeds 10%, one dose of a long-acting broad-spectrum parenteral antibiotic should be given while awaiting susceptibility data 7

Inpatient Management

• Hospitalization is recommended for patients who have severe illness or in whom complications are suspected 3
• Intravenous antibiotic options include extended-spectrum cephalosporins, fluoroquinolones, or penicillins 1
• Carbapenems and novel broad-spectrum antimicrobials should be reserved for patients with multidrug-resistant organisms 1

Treatment Duration

• A short outpatient course of antibiotic treatment for acute pyelonephritis is equivalent to longer therapy durations in terms of clinical and microbiological success, though this approach is associated with a higher recurrence rate within 4-6 weeks 2
• Typical treatment duration ranges from 7-14 days for adults 6

Complications

• Potential complications include:
  • Renal scarring (occurs in approximately 15% of patients after first episode) 1
  • Renal or perinephric abscess 1, 5
  • Acute kidney injury 5
  • Papillary necrosis 5
  • Emphysematous pyelonephritis 5
  • Long-term complications from renal scarring may include hypertension and chronic renal failure, though the risk is lower than previously thought 1

Prevention of Recurrence

• Women have up to a 10% risk of recurrent acute pyelonephritis in the year following a first acute episode, while men have a 6% risk 5
• Risk factors for uncomplicated acute pyelonephritis include recent sexual intercourse, acute cystitis, stress incontinence, and diabetes 5
• For patients with recurrent pyelonephritis, addressing modifiable risk factors and considering prophylactic antibiotics if non-antimicrobial interventions have failed may be considered 1

Special Populations

• Pregnant patients with pyelonephritis are at significantly elevated risk of severe complications and should be admitted and treated initially with parenteral therapy 7
• For imaging in pregnant women, ultrasound or MRI should be used preferentially to avoid radiation risk to the fetus 2
• In pediatric patients, ciprofloxacin is not a drug of first choice due to an increased incidence of adverse events, including events related to joints and surrounding tissues 6