When someone was positive, they tested every person that could have conceivably been in touch with...all positives were immediately identified and quarantined. This prevented asymptomatic people from spreading it, which is likely what happened in the US. At this point, in the US at least, the genie is out of the bottle...we have community spread. We can learn from Japan on how to handle the next one but we are already too late on this one.
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