Hi, the only way to pass your genital herpes is by sexual contact. It not spread by towels but needs direct rubbing contact to be at risk.
If I may add that at your parent's age, there must be upwards of 80% chance they already have HSV1. So even if the blood test is positive, this will not mean you spread it, which as noted is simply not possible given its genital location.
Thanks, turns out he was negative, was some kind of bacteria.