@merpreb My dentist's office says to buy them from a US company that tests them, and doesn't just accept the label. According to them, the ad should say something like "US tested." I just started looking for some - if I find what looks like a good source, I'll let you know.
Sue
PS Be wary of anyone selling "3M N-95 Medical Masks" - according to my sister who works there, even employees cannot buy them for personal use - the entire supply is committed to the medical industry - if you can find them you will pay a very high price per mask - in the area of $6-10 each (I used to pay $1.25 in quantity of 20.) You can still get a limited amount of the 3M industrial ones with exhaust port for yard work and similar - we see them at our paint stores, but again for a quite inflated price.