OK, so you never actually know how many cities might be related to a product?
If its not too late in the project I would look at creating a separate table for this data so you can have many cities to one product, rather than storing it as CSV data.
e.g. your Cities table would have a structure such as
cityid unique ID for the record
productidfk id that links to the product ID
cityname name of the city
then you can write a query to pull back the product and related city detail and filter it out as required.