I don't think you can get tetanus from touching a rusty object. Rust is not a pathogen.
The problem arises when a rusty, dirty object pierces your skin, so DON"T DO THAT.
"Spores of the bacteria that cause tetanus, Clostridium tetani, are found in soil, dust and animal feces. When they enter a deep flesh wound, spores grow into bacteria that can produce a powerful toxin, tetanospasmin, which impairs the nerves that control your muscles (motor neurons)." -- the InterWeb