EB> In Canada, prostitution is not, and never was illegal. Certain activities surrounding prostitution are, such as soliciting.
From my experience with talking with other SP's, MOST are concerned with their own health and will get checked regularly.
Notice I said most and not all, and I have not had the opportunity to talk with many street workers.
When I was working for agencies the question was never asked. In hindsight this does seem a little strange to me.
ALL sexually active people need to be responsible and get checked regularly for STD's, as well as get vaccinated for both hepatitus A & B (now available as a blended vaccine delivered in 3 shots, a month apart)
Personally I get checked a minimum of every six months.