Acute Pyelonephritis
A severe bacterial infection of the kidneys, usually ascending from the bladder, causing flank pain, high fever, and systemic illness.
Emergency Management: Pyelonephritis in the setting of an obstructing stone is an obstructive uropathy emergency, requiring immediate decompression (stent or nephrostomy tube) to prevent rapid destruction of the kidney and overwhelming sepsis.
Acute pyelonephritis is a bacterial infection of the renal parenchyma and renal pelvis, representing the most severe form of urinary tract infection (UTI). It typically ascends from the lower urinary tract and can lead to significant systemic toxicity, renal scarring, or sepsis if not managed promptly.
Detailed Overview
The infection almost always begins in the bladder (cystitis) and ascends via the ureters to the kidneys. The invading bacteria attach to the uroepithelium, triggering an intense local inflammatory response. This response involves neutrophil infiltration of the renal interstitium and tubules, causing localized edema and microscopic abscesses. Clinically, it is differentiated from simple lower UTIs by the presence of systemic signs like fever, chills, and flank pain. It is broadly categorized into uncomplicated (occurring in healthy, non-pregnant premenopausal women) and complicated (occurring in men, pregnant women, or patients with structural/functional abnormalities, immunosuppression, or indwelling catheters).
Epidemiology & Demographics
Incidence in the US is approximately 15-17 cases per 10,000 females and 3-4 cases per 10,000 males annually. Highest incidence is in young sexually active women, followed by infants and older adults.
Etiological Mechanism
Escherichia coli is the overwhelmingly predominant pathogen, causing 70-80% of uncomplicated cases. Other uropathogens include Klebsiella pneumoniae, Proteus mirabilis, and Staphylococcus saprophyticus. In complicated cases, Enterococcus species, Pseudomonas aeruginosa, and extended-spectrum beta-lactamase (ESBL) producers are more common.
Primary Causes
Ascending infection from the bladder (E. coli)
Hematogenous spread (rare, usually Staphylococcus aureus bacteremia)
Vesicoureteral reflux (VUR)
Obstructive uropathy (e.g., nephrolithiasis, BPH)
1. Uropathogenic E. coli colonize the periurethral area and ascend into the bladder. 2. P-fimbriae on E. coli bind to uroepithelial P-antigen receptors, preventing washout during voiding. 3. Bacteria ascend the ureters (facilitated by bacterial endotoxins inhibiting ureteral peristalsis) into the renal pelvis. 4. Infection enters the renal medulla and cortex, inducing an acute suppurative inflammatory response. 5. Neutrophils aggregate in collecting ducts and interstitial tissue, creating microabscesses. 6. Pro-inflammatory cytokines (IL-6, TNF-alpha) enter the bloodstream, causing systemic symptoms (fever, chills).
Diagnostic Criteria & Guidelines
Clinical diagnosis based on classic triad (fever, flank pain, CVA tenderness) supported by urinalysis demonstrating pyuria and bacteriuria. Urine culture is required to confirm the pathogen and susceptibility.
For mild/moderate uncomplicated cases (Outpatient): 1. Oral fluoroquinolones (e.g., Ciprofloxacin 500 mg PO BID for 7 days OR Levofloxacin 750 mg PO daily for 5 days) IF local resistance is <10%. 2. Alternative: Ceftriaxone 1g IV or IM x1, followed by Trimethoprim-sulfamethoxazole 160/800 mg PO BID for 14 days.
Second-Line & Adjunctive Therapy
For severe or complicated cases requiring hospitalization: IV antibiotics such as Ceftriaxone 1g IV daily OR Piperacillin-tazobactam 3.375g IV q6h. Step down to oral therapy once afebrile for 24-48 hours.
Surgical & Procedural Management
Generally medical. Urology intervention (ureteral stent placement or percutaneous nephrostomy) is required emergently if pyelonephritis occurs secondary to an obstructing kidney stone.
Patient Counseling & Advice
Emphasize completing the entire antibiotic course even if feeling better to prevent recurrence or resistance. Instruct to return if fever persists > 48 hours on antibiotics or if vomiting prevents keeping oral pills down.
Follow-Up & Monitoring Schedule
Clinical reassessment in 48-72 hours if no improvement. Repeat urine culture is not routinely needed post-treatment if symptoms fully resolve.
Preventive Strategies
For recurrent cases, continuous low-dose prophylactic antibiotics (e.g., Nitrofurantoin 50 mg daily) or post-coital prophylaxis may be considered.
Excellent with prompt and appropriate antibiotic therapy. Symptoms typically improve significantly within 48-72 hours. Mortality is low except in cases of septic shock or emphysematous pyelonephritis.