After her first urinary tract infection (UTI), a 1-year-old girl has a voiding cystourethrogram with findings shown below. Which of the following is the most appropriate treatment option?

The radiograph shows reflux into the ureters and into the kidney, with dilation of the renal pelvis, making the diagnosis of vesicoureteral reflux (VUR). The higher the reflux into the renal system, especially if the renal pelvis is dilated, the more likely it is for renal damage to occur; the grading system is based upon these radiographic observations. Grade I VUR is reflux of urine into an undilated ureter. Reflux into the ureter and collecting system without dilatation is called grade II. Grade III lesions have dilatation of the ureter and collecting system without blunting of the calyces. Grade IV lesions are characterized by blunting of the calyces, and grade V lesions demonstrate even more dilatation and tortuosity of the ureter. While somewhat controversial, low-grade lesions (grade I and grade II) usually are conservatively managed with close observation, daily low-dose antibiotics, and urinalyses and cultures every 3 to 4 months. Grade V lesions (and some grade IV lesions) require surgical reimplantation of a ureter if the findings persist. Lesions in between these two extremes are treatment dilemmas. Neither a diet low in protein nor early toilet training would likely affect the VUR.