There have been a few instances, IIRC there was an Apollo mission that had a head cold spread among the whole crew.

But that's unlikely to be the case here because they've been up there isolated for over 6 months now

> IIRC there was an Apollo mission that had a head cold spread among the whole crew.

Yep, Apollo 7.

Would it be possible for some food to have been contaminated with something? It seems unlikely.

this is what I'm thinking. GI related issues

This describes NASA's pre-flight quarantines since Apollo 14, and makes (very brief) references to in-flight diseases (and apparent transmission) prior to Apollo 14 ("upper respiratory infection"; "viral gastroenteritis"),

https://www.nasa.gov/wp-content/uploads/2023/12/ochmo-tb-006... ("Health Stabilization Program (HSP)")