A 2 weeks old girl presents with E-coli which is confirmed by urine culture. What is the most appropriate next investigation?

The key is US. [Infants and children who have had a lower urinary tract infection should undergo ultrasound (within 6 weeks) only if they are younger than 6 months or have had recurrent infections. Reference: NICE guideline (Probably to exclude VUR wich is a cause of recurrent UTI)].