Jonathan, it surprises many people to learn that rust has NOTHING to do with getting tetanus. Rust results when iron reacts with oxygen in air to form iron oxide - that's all. Tetanus is a bacterial disease caused by the bacteria named Clostridium tetani. This bacteria can form a surrounding, protective spore and live in the soil for over a thousand years. (was found in a rare Egyptian mummy). If the rusty nail or knife was lying in the soil before causing a DEEP penetrating wound through your skin, then you would have to consider the possibility of getting infected, but, hopefully you are a wise person who gets a protective tetanus immunization ("shot") every 10 years. BTW, the tetanus bacteria is destroyed by stomach and digestive acids and could not cause an infection if you swallowed any in your food. NOW, get a rust-free, clean knife which would not contain other bad bugs.