Deke Slayton: Jim, we've got a problem. I got some blood work back from the lab. Charlie Duke has the measles.
Jim Lovell: [Unconcerned] So we need a new back-up.
Deke Slayton: You've all been exposed to it.
Jim Lovell: Oh, I've had the measles.
Deke Slayton: Ken Mattingly hasn't.
The above scene from the movie Apollo 13 claims that Charlie Duke had a positive blood test for measles. Did he actually get sick? The IMDB FAQ page for the movie claims
The movie gives the impression that the Lunar-Module-to-Command-Module reverse power transfer and subsequent power-up sequence are masterminded by Ken Mattingly. The Ken Mattingly character as portrayed in the movie is in fact a composite character representing a team of people including Charlie Duke.
which suggests that he was healthy enough to help out. Of course, we know that Ken Mattingly was unaffected.