What are the common causes of bilateral pyelonephritis?

Common Causes of Bilateral Pyelonephritis

Escherichia coli is the most common cause of bilateral pyelonephritis, accounting for approximately 75% of all cases of recurrent urinary tract infections and pyelonephritis. 1

Microbial Causes

• Escherichia coli is the predominant pathogen, causing 70-90% of pyelonephritis cases 2
• Other common bacterial pathogens include:
  • Enterococcus faecalis 1
  • Proteus mirabilis 1, 3
  • Klebsiella pneumoniae 1, 2
  • Pseudomonas aeruginosa 1, 2
  • Staphylococcus saprophyticus (particularly in patients with risk factors for complicated UTIs) 1
  • Citrobacter species (diversus and freundii) 3
  • Enterobacter cloacae 3
  • Serratia marcescens 1

Risk Factors and Predisposing Conditions

Urinary Flow Disruption

• Vesicoureteral reflux (VUR) - particularly important in bilateral cases 1, 2
• Congenital urinary tract anomalies 1, 2
• Renal calculi (kidney stones) 1, 2
• Mechanical obstruction of urinary flow 1
• Altered bladder function 1

Anatomical and Functional Abnormalities

• Urethral or bladder diverticula 1
• Infected urachal cyst 1
• Postoperative changes (e.g., remaining urethral stump that retains urine) 1
• High postvoid residuals of urine 1
• Cystocele in postmenopausal women 1

Host Factors

• Diabetes mellitus 1, 2
• Pregnancy 1, 2
• Immunocompromised states 4
• Genetic predisposition 1
• Prior history of pyelonephritis (increases risk for recurrent episodes) 1
• Postmenopausal status with atrophic vaginitis 1

Behavioral and Other Factors

• Sexual activity, especially with a new partner 1, 2
• Use of spermicidal-containing contraceptives 1
• Personal or maternal history of UTIs 1
• Urinary incontinence in postmenopausal women 1

Pathophysiological Mechanisms

• Ascending infection is the most common route - microorganisms ascend from the urethra via the bladder into the upper urinary tract 2
• Hematogenous spread (blood-borne infection) occurs rarely 2
• P-fimbriated E. coli can cause ascending pyelonephritis even without vesicoureteral reflux due to paralytic effect on ureteral peristaltic activity 5
• Bacterial persistence can occur with:
  • Calculi (stones) 1
  • Foreign bodies 1
  • Anatomical abnormalities that cause urinary stasis 1

Special Considerations

• In children, bilateral pyelonephritis is often associated with congenital anomalies, particularly vesicoureteral reflux 1
• In neonates and young infants, there is a high incidence of urinary anomalies with UTI, with VUR being the most common 1
• Increasing rates of antimicrobial resistance, particularly extended-spectrum beta-lactamase (ESBL) producing organisms, are becoming a concern in both community and healthcare settings 2
• Bilateral pyelonephritis carries a higher risk of complications including renal scarring, which can lead to hypertension and chronic renal failure 1

Clinical Pearls and Pitfalls

• Bilateral pyelonephritis should raise suspicion for underlying structural or functional abnormalities of the urinary tract 1
• Not all patients with pyelonephritis present with fever - absence of fever does not exclude the diagnosis 1
• Patients with bilateral pyelonephritis are at higher risk for sepsis and should be evaluated promptly 4
• Imaging studies are indicated in bilateral pyelonephritis to detect treatable conditions and monitor progress 1
• Urine culture should be obtained before initiating antibiotic therapy to guide treatment 4