They are certainly tested. My father in law was in after having a heart attack and was tested. 3 on his ward were positive.
So if these people hadn't gone into hospital for another reason they possibly would not have been tested? Maybe they wouldn't have tested positive as they could have picked it up in the hospital... maybe?
The point I'm trying to make is that to say the number of people who have been admitted with Corona virus is..... isn't really true is it?