Imaging after a first febrile UTI in infancy

A febrile urinary tract infection in an infant is treated as pyelonephritis. It matters because a proportion of these babies have an underlying abnormality, most often vesicoureteric reflux or an obstructed system, and because repeated infections can scar the kidney.

Imaging after a first infection has become much more selective. A first, typical E. coli infection in a child over 6 months who responds within 48 hours does not need routine imaging. Ultrasound is reserved for atypical infection, recurrent infection, and infants under 6 months who have not had antenatal scans to exclude a renal tract abnormality. Atypical features are a non-E. coli organism, failure to respond within 48 hours, a seriously unwell or septic child, a poor urine stream, an abdominal or bladder mass, and a raised creatinine. Klebsiella makes this infection atypical, so a renal tract ultrasound is indicated. It is non-invasive, involves no radiation, and detects hydronephrosis, dilated ureters, bladder abnormalities and differences in kidney size. In an atypical infection it is done during the acute illness or soon after discharge.

A micturating cystourethrogram (MCUG) is the test for vesicoureteric reflux, but it involves catheterisation and radiation, so it is reserved for children with an abnormal ultrasound, recurrent febrile infections, an atypical organism, or a family history of reflux.

A DMSA scan looks for renal scarring and is done 4 to 6 months after infection, not acutely, and only in selected children with recurrent or complicated infection.

Prophylactic antibiotics are not recommended after a single infection, because they give little benefit and promote resistance. Parents should be told to seek urine testing early with any future unexplained fever.