A Seattle hospital is warning that lapses in its hepatitis B virus (HBV) screening procedures may have put more than 650 dialysis patients at risk of infection over the last five years, Tech Times reports.

According to health officials in Washington, some staff members at Virginia Mason Hospital have been inconsistent in screening and isolating patients treated in the hospital’s three-bed dialysis unit since 2011. Currently, the U.S. Centers for Disease Control and Prevention (CDC) recommends that HBV-positive patients be treated in a private room, away from other patients. However, Virginia Mason apparently didn’t do that and was recently called out by a local nonprofit accreditation company.

Although hospital officials have found no evidence that any diseases were transmitted, they are urging more than 650 patients to get tested for hepatitis B if they have not already. Public health officials likewise said that the risk of transmission is low, because most chronic kidney disease dialysis patients are already regularly screened for HBV.