Can UTI occur in the absence of pus cells?

It is highly unlikely that you have a UTI in absence of pus cells. The number of pus cells would be high with infection, though the concentration may vary with urine dilution depending on water intake. In absence of pus cells or symptoms such a positive urine culture is more likely to be urine contamination with bacteria. I would strongly suggest you to have both urine examination and culture repeated from another microbiology lab.