It can't be easy for any cruise line to know the total number of passengers stricken with a gastrointestinal virus because not all infected report to the Medical Centre. But "The CDC requires "an immediate special report … when the percentage of gastrointestinal illness cases in either passenger or crew reaches 2 percent," wrote Vazquez, a CDC health communication specialist, in an e-mail." quoted from http://www.sun-sentinel.com/business...,3050426.story
I don't know how many passengers or crew members are currently on board QM2, but if 2% of either are stricken, my guess is that the CDC website* would reflect that information - and currently there is no mention of an outbreak on QM2 (not to doubt that there is a problem, only that it appears not to have reached the 2% threshold). Of course, that doesn't explain why the passengers on board have not been informed of the reported number of cases to date, thus quelling any speculation.
Best wishes to all concerned. Regards, -S.