Obviously, mosquitoes do not know anything about following boundaries. I believe the explanation in large part for the discrepancy is that many or most people have gone to the French side for testing. I am not at all sure whether this is because the equipment is thought better on the French side, less costs, or what the explanation is, but I think the explanation has to do with the fact that it is not a confirmed case unless there are test results and most people are going to the french side for the test.

The epidemic is past its peak for SXM as a whole yes, but there will continue to be issues with it so long as there are mosquitoes.