This is a common concern, but the short answer is no—HIV cannot be spread this way. It is scientifically impossible to contract HIV from a knife used in food preparation, even if the person who used it before you had an untreated viral load.

Here is why you don’t need to worry:

HIV is 'Fragile': The virus is very weak once it leaves the human body. As soon as blood is exposed to air and the cooler temperature of a kitchen surface, the virus begins to break down and loses its ability to infect.

The Route of Entry: HIV needs a direct 'doorway' into your bloodstream. Even if you ate a sandwich made with that knife, your digestive system is designed to protect you. Your stomach acid is incredibly strong and would destroy the virus before it could ever enter your system.

Environmental Barriers: Saliva and the enzymes in your mouth also act as natural barriers. There has never been a documented case of HIV being transmitted through food or sharing kitchen utensils in the history of the epidemic.

A Note on General Safety: While HIV isn't a risk here, it is always a good idea to wash any kitchen tools with hot, soapy water if they come into contact with blood. This is just standard kitchen hygiene to protect against much hardier germs, like bacteria or other viruses (like Hepatitis), which can survive longer on surfaces than HIV can.

You are safe, and the sandwich is safe!