I live in Alberta and the same thing happened to me.I ordered 2 more packages and am also wondering if I should start from scratch or what.

Not too sure myself what is best....probably the right thing to do is, have a frame of old brood comb examined by expert
for any sign of sickness or foulbrood spore count?
Konrad

Try searching for info about this: imidacloprid insecticides
It is the currently the world's most common pesticide and used quite liberally. Except some parts of Europe have banned it's used because links to CCD (one of the actions it has is compromising an insect's immune system, which is thought to leave bees open to diseases that have been present all along)

I haven't had luck yet figuring out how to clean hives after this occurs. But I suspect if imidacloprid is the main contributing factor leading to their vulnerability to pathogens, it won't make much difference if it's still being used in the area. It's marketed under many names and is also in lawn grub treatment - and commonly used in golf courses, etc.