I wish a GS resident or attending would comment on this.
Comment on what, exactly?
Where I went to med school, students were specifically barred from scrubbing in on HIV/HepC/HepB patients. The school was very clear about this, although patients were not routinely tested, but on rotations off-site (we got sent out to other locations for some rotations), this was not enforced. Some faculty at the main hospital took this one step further, and wouldn't even let us round or care for such patients.
In my residency program, students were NOT exempt from caring for or scrubbing in on these patients. (no routine screening, either). Sometimes we would try and give the student a pass on scrubbing, if it was bound to be a difficult/painful case, but if the attending asked about the student.... Also, certain rotations had a higher risk of this (like transplant or vascular, with dialysis patients and ESLD patients with a high incidence of HepC) so students assigned to those rotations usually couldn't refuse.
Personally, as an attending, I am inclined to let the student decide if they want to scrub and make it clear I'm not "testing" them by giving them an option. If the student is interested in participating in the case and knows the HIV/HepC status, the student can make his/her own decision on that. Afterall, any patient *could* have something bloodbourne...in these patients, we just know it for a fact.