<prompt> Influenza pandemic is mainly caused by -Type AType BType CAll  <response>: Influenza Influenza is an acute respiratory tract infection caused by influenza virus.There are three viral subtypesType A Causes all Pandemics and most of the epidemicsType B Can cause epidemicsType C Causes endemic infectionThree types of influenza viruses are circulating in world A H1N1, A H3 N2 and BA New type has been recognized A H5 N1Source of infection case or subclinical caseMode of transmission Droplet infection by respiratory routeIncubation period 18-72 hoursClinical manifestationsMost infections are subclinicalfever, headache and myalgiaRespiratory coughingThere is no virerniaComplicationsPneumonia M.C. by str. pneumoniaeWorsening of COPDEncephalitisReyes Syndrome with type B virusGB. SyndromeG I Symptoms gastric flu type B virusLaboratory diagnosisMost commonly, the diagnosis is established by the use of rapid viral tests that detect viral nucleoprotein or neuraminidase - Harrison - 1069Best specimen is nasopharyngeal secretion. 