Regular starter Matt Schaub fell ill Saturday and spent the night in an area hospital with a viral infection.
Schaub was at Reliant Stadium and active for the game and was not mentioned in the Texans' initial lineup changes. But the team later confirmed Rosenfels would start.
The Texans don't have a third quarterback. Tight end Owen Daniels is the team's emergency option.
Paul Kuharsky covers the AFC South for ESPN.com.