A Children's National Hospital health-care worker holds a vial containing a swab at a drive-through coronavirus testing site at Trinity Washington University in the District. (Andrew Harrer/Bloomberg News)

At some Maryland hospitals where vascular surgeon Roger Schneider operates, he knows how many staff members have tested positive for the novel coronavirus, how many patients have the virus that causes covid-19 and in what units they are being treated.

At other hospitals where he does surgeries, he is less sure.