Even testing 100 people would still be informative and give you an upper and lower bounds on the number infected. You don't need an exact number to form policy.
Can't you see how these factors mean that testing 100 people would not lead to a proper representative sample?
I don't think 100 people would be enough to properly and statistically test for a common cold, much less for a disease like this.
Where did I ever write this? I wrote it would give us an upper and lower bound.