I don't really know. I have an educated guess for the custom format though. They started collecting data before XML, JSON, etc were widely used and/or existed which explains the custom text format. Since their systems already handle their custom format, there is no real incentive to change it.
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Can you answer why it's so bad?
I can guess at a lot of answers but which particular strain of corporate pathology CDC suffers from
I don't really know. I have an educated guess for the custom format though. They started collecting data before XML, JSON, etc were widely used and/or existed which explains the custom text format. Since their systems already handle their custom format, there is no real incentive to change it.