Infections by certain strains of E.coli which release O antigen may paralyze the ureter causing a functional obstruction. Other strains of E.coli have fimbriae which provide them with mobility. Higher grades of reflux are a risk factor for pyelonephritis, but in patients with mild reflux, their risk for pyelonephritis is the same as in those without reflux. Infants with pyelonephritis typically present with fever, lethargy, irritability, and failure to thrive. Toddlers may present with fever, abdominal pain, vomiting, diarrhea, and feeding problems.
Older children are more likely to have the typical adult symptoms of fever, chills, and flank pain.
E. coli , Proteus , and Klebsiella are the common inciting organisms. The resultant ischemia has been postulated as one of the mechanisms for the decreased accumulation of DMSA in areas of pyelonephritis. Later there is the formation of micro-abscesses and suppurative necrosis. Most cases of acute pyelonephritis resolve without scarring. In patients with renal scarring, scars are identified only at sites corresponding to previous areas of acute pyelonephritis.