Quite some years ago testing was carried out for the first time [ that I can recall ] at Riccarton, and the results of that, and some north island areas as well, led the then Racecourse ' D' to quip that if all the positives were suspended or disqualified, there would be many stables with no staff at all.
So some were not permitted to ride work, but were able to continue with their groundwork duties.
Different ball game now I feel....and yes, Jess, not just restricted to staff either.