This is an interesting hypothesis from a medical professional regarding a root cause of the current influenza epidemic in the US as well as the Norovirus too.
[link to www.promedmail.org]

"My hunch is that we can tie some of the impact of influenza this year [2012-2013] to Hurricane Sandy. I started thinking about this during a meeting with my MN1-DMAT [Minnesota-1, Disaster Medical Assistance Team]. It was triggered by a comment about an outbreak of norovirus at the medical shelter that my team was staffing.

I started thinking that maybe the use of shelters during the hurricane brought a lot of people in much closer proximity to each other at a time when influenza was just starting to ramp up for the year but not at a time when it was symptomatic. There was clear evidence of transmission of Spanish flu during the 1918 pandemic over the summer and that it had mutated substantially during those months. I am not arguing that there was any mutation due to Hurricane Sandy but strictly that there was probably a lot of transmission in those close quarters."

More at the link above.