• Most commonly caused by aerobic gram negative organisms including E. coli, Proteus, and Pseudomonas.
  • Gram positive organisms like Staphylococcus saprophyticus and enterococci are less common.


Patients usually presents with an acute onset of fever, chills, flank pain and irritative voiding symptoms. They often look quite ill. Percussion of the ipsilateral costovertebral angle elicits significant pain. Urinalysis shows heavy pyuria, bacteruria, mild proteinuria and often microscopic haematuria.

Differential Dx


  • Testicular pathology
  • AAA
  • Sepsis (± ureteric obstruction)
  • Pneumonic / lower lobe pathology
  • Cholecystitis


Mild to moderate pyelonephritis can be treated on an outpatient basis with fluoroquinolones such as Ciprofloxacin. More severe or complicated cases require admission to hospital with early upper tract imaging and wide spectrum antibiotics such as Ampicillin and Gentamicin.

Please see the antibiotic guidelines (HSESouth) page.

Content by Dr Íomhar O' Sullivan 11/05/2005. Reviewed by Dr ÍOS 26/05/2006. Last review Dr ÍOS 5/05/15