EnzymeimmunoassayforthequalitativedeterminationofIgAclassantibodiesagainstInfluenzavirusAinhumanserumorplasma(citrate).InfluenzaareRNAvirusesofthefamilyOrthomyxoviridae.Influenzavirusesaredividedintothreetypes,designatedA,B,andCwhicharedifferentiatedbythespecificityofasolubleantigenassocia-tedwiththeinternalribonucleoproteincomponentofthevirion.Thevirionsarespericalparticlesof80-120nmindiameterconsistingoftheribonucleoproteincomponentandenvelopedbymatrixproteinandalipidbilayerwhichcontainstwospikelinestructures:viralhemagglutinin(H)andviralneuraminidase(N).Influenzavirusesarerespiratorytractpathogenswhicharetransmittedbydirectcontact,large-dropletinfection,orbycontaminatedsurfaces.InfluenzytypesAandBareresponsIBLeforepidemicsofrespiratoryillnessthatoccuralmosteverywinterandareoftenassociatedwithincreasedratesofhospitalizationanddeath.TypeCinfectionsusuallycauseeitheraverymildrespiratoryillnessornosymptomsatall;itdoesnotcauseepidemicsanddoesnothavetheseverepublichealthimpactthatinfluenzatypesAandBdo.PandemicsofinfluenzavirustypeAinfectionshaveoccuredat10to20yearintervalssince1890.ApparentlythisresultsfromalterationsinthecompositionoftheHandNantigens(antigenic“drift”andantigenic“shift”).CurrentlytwosubtypesofinfluenzaAarecirculatingworldwide.Normallyinfluenzaisaself-limitingdiseaselastingfor3to7days,butsomepeopledevelopseriousandpotentiallylife-threateningmedicalcomplications,suchaspneumonia,particularlyinchildren,elderlypeopleandothervulnerablegroups.