Dragon Ball discussion: How did Goku catch the heart virus?

Here's a question that hardly any Dragon Ball fan asks. Just how did Goku catch the heart virus? We all know that Trunks travels through time to give Goku the medicine that saves his life from the virus, but it's never explained just how he got it. It couldn't have been on Namek, since no else who was there got sick. Unless that healing tank wasn't too clean, but I still think it's unlikely. I say Goku must've gotten the virus while in space, maybe on while on Yardrat. This is just for fun, but I want to hear what you guys think.