If by "original game" you mean the version made in 48 hours for Ludum Dare, just download "serum_run_COMPO.exe" from the downloads page. Sorry, I guess the meaning of "compo" is not clear for people not familiar with Ludum Dare.
Publishing on Steam would cost me $100, and so far I have made precisely zero dollars from this game, so there is no plan to publish on steam at this point.