Hello,
I am currently on Version 1.19.155463, and it appears that illness from consuming damaged cans of food, or generic food poisoning, including chemical, doesn't resolve after taking charcoal tablets, tetracycline, vitamins, rest, or keeping your health and water in a stable state to develop natural immunity.
As a result of this, your character will currently and permanently remain ill. More then likely, the bug occurs as a result of two, simultaneous infections, or an update in the game which alters severity and duration with the unintended result that this lasts permanently.
Currently on MI4218. Character has been sick going on three actual days without resolution. In-game days is close to 14, in lieu of taking medications.
We also should have an indicator which reflects how many active illnesses we have so that we know when one resolves or not, but as of right now, poisoning and sickness is a broken mechanic.