Pyelonephritis is an infection of the kidney. Most cases of pyelonephritis are caused by ascent of bacterial pathogens (usually gram-negative bacilli but occasionally gram-positive organisms such as Enterococcus species) from the bladder to the kidney.

Patients with abnormalities of the urinary tract (including children with vesicoureteral reflux) are at increased risk for this infection. Pregnancy and renal transplant also increase the risk of pyelonephritis.

Patients with bloodstream infection with certain pathogens including Staphylococcus aureus or Candida species are at risk for hematogenous seeding of the kidneys.

Patients present with flank pain and fever. There are often associated urinary symptoms including dysuria, urgency, or frequency. Gross hematuria may occasionally be seen. Patients with spinal cord injury or dementia may present atypically, but fever is expected to be present in cases of pyelonephritis. Examination will reveal costovertebral angle tenderness.

Rare complications of pyelonephritis include papillary necrosis, renal abscess, and perinephric abscess.

Related topic: urinary tract infection