I only reported this as is (with mods) because I happened to have a clip of it during regular gameplay, it'd be tricky to easily repro as it seems like it's an uncommon thing to happen.
The only traits I can think would have caused this are the Immunocompromised (more traits mod), slow healer, prone to illness, very underweight. Looking at the code for immunocompromised it only affects your chances of infection. I checked and Infection Mortality is also not set to instant just in case that was taking effect despite zombification being disabled.
I'm not sure how I can help repro this without mods as it's just going to be a random chance