- BK virus- Patients post transplant may develop asymptomatic BKV viruria or viremia. BK reactivation will be defined as detection of elevated BK levels by PCR in blood or urine while disease will be defined as detection in multiple sites or in one site with symptoms. Cidofovir has been administered intravenously in a low dose (i.e. up to 1 mg/kg 3 times weekly, without probenecid) or a high dose (ie, 5 mg/kg per week with probenecid) to HSCT patients with BK infections but no randomized trials are available proving its clinical efficacy. In patients who meet the criteria for disease Cidofovir may be added unless the subject could not tolerate this agent due to nephrotoxicity.