The start of pandemics: site, season and spread.
D000349:Africa; D002681:China; D004196:Disease Outbreaks; D049671:History, 18th Century; D049672:History, 19th Century; D049673:History, 20th Century; D006801:Humans; D007251:Influenza, Human / Q000266:history*; D010176:Panama; D012425:Russia (Pre-1917); D012621:Seasons; D014481:United States