My 3 month old son was born with hydronephrosis and his pyleoplasty operation was done at 1.5months of age. After a month the DJ stent was also removed and all was well. But now after 2weeks of operation he developed a UTI with pus cells around 50-60 and E.coli detected in culture. He was put on antibiotics and mikacin injection for 5days. After the course of medicine, culture shows negative while pus cells around 40-50 still. What does this signify?? Please help