Swine flu starts during flu season,sometimes,but usually it is a freak thing which means it just pops out of nowhere. Swine flu comes from pigs,which is why everyone calls it "SWINE" flu. Analysis has suggested that the H1N1 strain responsible for the current outbreak first evolved around September 2008 and circulated in the human population for several months before the first cases were detected. Get more info on the Flu Wiki at flu.wikia.com.