When the Disease: Gut Worms incident occurs, the message lists the names of affected colonists. However, it also lists colonists who have bionic stomachs, even though they are not affected by gut worms.
Colonists who are unaffected shouldn't appear in the message.
To reproduce: Give some/all colonists bionic stomachs. Wait for gut worms to occur. Or use dev mode and force it to occur.
I see this being like pawns who are Penox and are chosen for Malaria, Flu, Plague. It's not that they don't get it, it's that it's blocked by the drug. If there isn't, there should be a message popping up in the upper left corner (same spot as "<raid faction> is beginning their assault") saying the stomach blocked the gut worms. I know there is a message for those that Penox blocks.
A separate message would work too, but no, there wasn't one.
Thanks for the bug report. I agree with StlyAU here. I think what is happening is that the pawn with a bionic stomach *would* have gotten the gutworms, but avoided it because they had a bionic stomach. It probably should be made more clear though, so I'll add a report in to the devs to create a message similar to the penoxycylin addendum.