Contact tracing is carried out all the time, both voluntarily where some one who tests positive engages with health services or by compulsion where someone has knowingly put others at risk of their pre-diagnosed position. (A criminal offence under UK law.)

National Aids Trust.
"Partner notification, the process of contacting the sexual partners of someone diagnosed with HIV, is a highly effective way of getting people tested and diagnosed. Audits show up to 37% of partners traced and tested through this process were diagnosed HIV positive as a result.7 Despite this, the role of partner notification in prevention and testing is neglected and under resourced; this should be addressed in a future strategy."