The rapid field tests are unreliable. The reliable tests take several days to get results. Or that is what I read yesterday via some news story in which the person quoted seemed to be knowledgeable.
It has taken days to obtain results in the suspected U.S. cases. This is why it drives me crazy when I hear some talking head on TV say that people coming off African flights are being "tested." We already see it isn't like pricking a diabetic's finger and getting instant results---there IS no quick test.
I suspect they're having their temperatures taken, which reveals nothing.