Two interpretations are obvious; pollution and/or initiation. When it is a one-off thing, it is probably a contamination of your spirit, but if it is regular, it points to the fact that such a person has a demonic covenant with some secret societies.
At other times, it could be a demonic attack to introduce a terminal disease into the life of the person.
- I purge myself with the Holy Ghost fire 7x
- I command demonic night caterers to be roasted by fire
- I fence myself henceforth with the wall of fire!