Don't ask, don't ask

From some snake-oil commercial:

"Ask your doctor if you live in or have been to a region where certain fungal infections are common."

In that context, what does the word "certain" mean? Definite? Particular??

And how does it work?

1. Doc, do I live in -- or have I been to -- a region where definite fungal infections are common?

Are doctors often sure that infections are fungal?

Or

2. Doc, do I live in -- or have I been to -- a region where particular fungal infections are common?

Do any fungal infections occur often in the region?