Please do not panic - the real-world risk here is extremely small. In clinics and hospitals disposable auto-lock syringes are the norm now, and re-use of a syringe on two people is very rare. Even in a documented needle-stick with an infected person's blood, the risk of
HIV is under 0.3 percent, hepatitis C about 1.8 percent, and hepatitis B is the highest but is preventable by vaccination. With an unknown and most likely clean needle, your risk is negligible. Still, for your peace of mind, the correct approach is simple testing. Get an HIV 4th generation antigen/antibody (HIV Duo) test, HBsAg and anti-HCV done now as a baseline, and repeat HIV Duo plus anti-HCV at 6 weeks and again at 3 months from the date of the injection - a negative HIV test at 3 months rules it out conclusively. If you are not already vaccinated against hepatitis B, take the vaccine schedule (0, 1 and 6 months) irrespective of this incident, as it protects you lifelong. Do also check anti-HBs 1-2 months after the last dose to confirm protection. In future you may simply ask the person to open a fresh syringe in front of you - it is a reasonable request. There is no need for any medicine or post-exposure prophylaxis at this stage since the exposure was a week ago and of unknown, very low risk. If you develop fever with rash, jaundice, yellow urine or persistent fatigue, get reviewed sooner. I am available on Practo consult or at Synergy Multispeciality Hospital, Miraj if you want to go over your reports.