['We evaluated the influence of patient factors and virulence factors of uropathogenic Escherichia coli on the occurrence of acute pyelonephritis and subsequent renal parenchymal scarring.', 'We evaluated 80 boys and 45 girls 1 to 180 months old with febrile urinary tract infections who underwent renal scan to diagnose acute pyelonephritis and followup dimercapto-succinic acid scintigraphy at least 6 months later. Urinalysis, white blood cell count, uropathogenic E. coli genotype and vesicoureteral reflux were measured. Voiding cystourethrogram was investigated after acute pyelonephritis was confirmed by renal scan and acute inflammation subsided, about 2 to 4 weeks later.', 'Acute pyelonephritis was significantly more likely to develop in children with urinary tract infections and persistent fever before and after hospitalization, elevated C-reactive protein or positive renal ultrasound findings. E. coli strains with the papG II and iha genes were significantly more likely to occur in patients with acute pyelonephritis. Patients with a fever for more than 3 days and C-reactive protein levels greater than 90.8 mg/l were significantly more likely to have renal scarring. Age was not an independent predictor of acute pyelonephritis, but modified the effect of virulence factors on the development of acute pyelonephritis.'] Are bacterial virulence factors associated with occurrence of acute pyelonephritis but not renal scarring?