Pyelonephritis: Kidney Infection Symptoms, Causes, and Treatment

Definition

Pyelonephritis is a bacterial infection of the renal pelvis and parenchyma—an upper urinary tract infection (UTI).

Typical Presentation

• Flank/back pain (unilateral or bilateral)
• Fever, chills, rigors
• Dysuria, frequency, urgency
• Nausea, vomiting
• Costovertebral angle tenderness

Etiology

Most commonly E. coli ascending from the bladder. Risk factors: female anatomy, sexual activity, urinary obstruction, catheterization, diabetes, immunosuppression, vesicoureteral reflux.

Management

• Outpatient: Oral antibiotics (fluoroquinolone or TMP-SMX) for 7–14 days if mild-moderate, reliable follow-up.
• Inpatient: IV antibiotics (ceftriaxone, piperacillin-tazobactam) for severe sepsis, obstruction, pregnancy, or inability to tolerate oral.
• Hydration, analgesia, antipyretics.
• Imaging (CT) if no improvement in 48–72 h or suspicion of abscess/stone.

Prompt treatment prevents sepsis, renal scarring, and chronic kidney disease.