Hi..
Welcome to HEALTHCARE MAGIC..
I have gone through your query and can understand your concern..
As per your complain as you have history of allergic rhinits leading to
post nasal drip and
cough, it is not a communicable disease as it is not due to infection and allergies are not communicable..
I would suggest you to consult an Otolaryngologist and get tested for any bacterial or viral infection..
In case if there is infection also then you will have to take precaution and should not kiss of eat with your grandson to prevent infection and also you should take treatment to resolve the infection like Antibiotics, decongestants, mucolytics etc..
In case if it is completely due to
allergic reaction and no infection involved, it is safe for you to be around your grand son and will not cause him any harm..
Hope this information helps..
Thanks and regards.
Dr.Honey Nandwani Arora..