Although historically sterile pyuria has been associated with genitourinary (GU) tuberculosis, there are many more common causes to consider in the hospitalized patient. 

Recent antibiotic exposure (within past 2 weeks) in the setting of UTI is one of the most frequent causes.  Prostatitis is also an often overlooked cause.  About 15% of hospitalized patients with systemic infections outside of the GU tract (e.g. pneumonia) may also have sterile pyuria. Non-infectious causes include current or recent catheterization of bladder, urinary stones, stents, GU malignancy, papillary necrosis,  and analgesic nephropathy. 

I would start out with a prostate exam.

Reference:

Wise GJ, Schlegel PN. Sterile pyuria. N Engl J Med 372;11:1048-54.