Why do I keep getting anxiety and fear over the possibility of catching HIV?

I understand where you're coming from but HIV/HCV testing methods have been implemented for years and as a result this has significantly decreased the chance of someone contracting a disease through blood transfusion. Perhaps you have OCD (Obsessive Compulsive disorder) or some other psychological disorder. It's perfectly normal to have fears but these fears are really irrational. Again, it's perfectly normal to be cautious but in this case, the possibility of it is close to zero. Good luck and I wish your partner a speedy recovery.