I was just thinking about this while playing, I got a lot of "A dog bit me" lines and I thought it'd be cool if you could ask the survivors as your checking for signs of infection. For example:
Q: How did you get these scratches/bruises?
A: I fell on rocks...I'm NOT infected!
Another cool thing to add would be more aggressive sounding dialog, since that's a sign of infection like while your taking the temperature of someone you could ask "How was your day?" and depending on what the survivor says we can determine if they are infected or not by words, unless of course the survivor in question has an aggressive personality.