It probably means that surveillance in Mexico is poor and there has been many many more who have had the virus but because of its current mild nature have not presented at surgeries or hospital.
As I understand it the 1600 thay refer to as possible patients are those who have been admitted to hospital.
To put it in perspective there are 35,000 deaths per annum from flu related causes in the US...(or so CNBC tells me)
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BTA Price at posting:
$1.60 Sentiment: LT Buy Disclosure: Held