While there is no specific data related to blood splotches in toilet paper, the Centers for Disease Control and Prevention states that a person has a 1 in 160 chance of contracting HIV if they were to share a needle that was used by someone who has HIV. Furthermore, per Healthline, HIV is very fragile once it reaches an outside environment, and unless there are very specific conditions with temperature, humidity, and other environmental factors that could keep the virus active for longer, it is unlikely that you can contract HIV from sitting on a toilet seat. Syringes are a different story, however. Per the Centers for Disease Control and Prevention, HIV can remain active in a used syringe for up to 42 days if conditions are favorable.
The hepatitis virus, on the other hand, is a lot more hardy, so to speak. Per the World Health Organization, it can survive outside of the body for an entire week and can cause infection if it enters the body of someone who isn’t vaccinated.
All this to say, perhaps the lesson with such viral TikTok videos is to be more aware of your surroundings. Look at the toilet paper you’re about to use when you’re at a public restroom. Does it look questionable? Then don’t use it. As for carrying a toilet paper roll with you, that habit never hurts, either. You never know when some toilet paper will come in handy.