<prompt> Shoest incubation period is seen inHepatitis AHepatitis BRubellaInfluenza  <response>: Influenza Causative Agent: Ohomyxovirus, 3 types : A, B, C Type A: MC cause of outbreaksEpidemics ; Only cause of Pandemics Type B. Type C: Not circulating currently Incubation period : 18-72 hours Period of Infectivity : 1-2 days before to 1-2 days after onset of symptoms Ref:Parks Textbook of Preventive and Social Medicine 25th Edition Pgno : 167-172 