What makes you think it was Nosema? All confined bees get dysentery, if that was your criteria. A microscope is the only way to tell if they have Nosema. Nosema apis seems to have virtually dissappeared, and that was the variety that sometimes caused dysentery (not the only cause as any confined bees will have dysentery if they are feeding brood and confined very long). If it is Nosema ceranae the spores tend to die in the cold.
"The infectivity of N ceranae spores dropped substantially after a week of refrigeration, and dramatically after a week of freezing. Modified from Fries (Bitidningen 107, 2009) by permission."--Randy Oliver (see above link)
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