Influenza (Seasonal) - WHO | World Health Organization

Seasonal influenza is characterized by a sudden onset of fever, cough (usually dry), headache, muscle and joint pain, severe malaise (feeling ... Home/ Newsroom/ Factsheets/ Detail/ Influenza(Seasonal) WHO/T.Pietrasik © Credits Influenza(Seasonal) 6November2018 Asktheexpert:InfluenzaQ&ASeasonalinfluenzaisanacuterespiratoryinfectioncausedbyinfluenzaviruseswhichcirculateinallpartsoftheworld.ThepathogenThereare4typesofseasonalinfluenzaviruses,typesA,B,CandD.InfluenzaAandBvirusescirculateandcauseseasonalepidemicsofdisease.InfluenzaAvirusesarefurtherclassifiedintosubtypesaccordingtothecombinationsofthehemagglutinin(HA)andtheneuraminidase(NA),theproteinsonthesurfaceofthevirus.CurrentlycirculatinginhumansaresubtypeA(H1N1) andA(H3N2)influenzaviruses.TheA(H1N1)isalsowrittenasA(H1N1)pdm09asitcausedthepandemicin2009andsubsequentlyreplacedtheseasonalinfluenzaA(H1N1)viruswhichhadcirculatedpriorto2009.OnlyinfluenzatypeAvirusesareknown tohavecausedpandemics.InfluenzaBvirusesarenotclassifiedintosubtypes,butcanbebrokendownintolineages.CurrentlycirculatinginfluenzatypeBvirusesbelongtoeitherB/YamagataorB/Victorialineage.InfluenzaCvirusisdetectedlessfrequentlyandusuallycausesmildinfections,thusdoesnotpresentpublichealthimportance.InfluenzaDvirusesprimarilyaffectcattleandarenotknowntoinfectorcauseillnessinpeople.SignsandsymptomsSeasonalinfluenzaischaracterizedbyasuddenonsetoffever,cough(usuallydry),headache,muscleandjointpain,severemalaise(feelingunwell),sorethroatandarunnynose.Thecoughcanbesevereandcanlast2ormoreweeks.Mostpeoplerecover fromfeverandothersymptomswithinaweekwithoutrequiringmedicalattention.Butinfluenzacancausesevereillnessordeathespeciallyinpeopleathighrisk(seebelow).Illnessesrangefrommildtosevereandevendeath.Hospitalizationanddeathoccurmainlyamonghighriskgroups.Worldwide,theseannualepidemicsareestimatedtoresultinabout3to5millioncasesofsevereillness,andabout290000to650000 respiratorydeaths.Inindustrializedcountriesmostdeathsassociatedwithinfluenzaoccuramongpeopleage65orolder(1).Epidemicscanresultinhighlevelsofworker/schoolabsenteeismandproductivitylosses.Clinicsandhospitalscanbeoverwhelmedduringpeakillness periods.Theeffectsofseasonalinfluenzaepidemicsindevelopingcountriesarenotfullyknown,butresearchestimatesthat99%ofdeathsinchildrenunder5yearsofagewithinfluenzarelatedlowerrespiratorytractinfectionsarefoundindevelopingcountries (2).EpidemiologyAllagegroupscanbeaffectedbuttherearegroupsthataremoreatriskthanothers.Peopleatgreaterriskofseverediseaseorcomplicationswheninfectedare:pregnantwomen,childrenunder59months,theelderly,individualswithchronicmedicalconditions(suchaschroniccardiac,pulmonary,renal,metabolic,neurodevelopmental, liverorhematologicdiseases)andindividualswithimmunosuppressiveconditions(suchasHIV/AIDS,receivingchemotherapyorsteroids,ormalignancy).Healthcareworkersareathighriskacquiringinfluenzavirusinfectionduetoincreasedexposuretothepatientsandriskfurtherspreadparticularlytovulnerableindividuals.Intermsoftransmission,seasonalinfluenzaspreadseasily,withrapidtransmissionincrowdedareasincludingschoolsandnursinghomes.Whenaninfectedpersoncoughsorsneezes,dropletscontainingviruses(infectiousdroplets)are dispersedintotheairandcanspreaduptoonemeter,andinfectpersonsincloseproximitywhobreathethesedropletsin.Theviruscanalsobespreadbyhandscontaminatedwithinfluenzaviruses.Topreventtransmission,peopleshouldcovertheir mouthandnosewithatissuewhencoughing,andwashtheirhandsregularly.Intemperateclimates,seasonalepidemicsoccurmainlyduringwinter,whileintropicalregions,influenzamayoccurthroughouttheyear,causingoutbreaksmoreirregularly.Thetimefrominfectiontoillness,knownastheincubationperiod,isabout2days,butrangesfromonetofourdays.DiagnosisThemajorityofcasesofhumaninfluenzaareclinicallydiagnosed.However,duringperiodsoflowinfluenzaactivityandoutsideofepidemicssituations,theinfectionofotherrespiratoryvirusese.g.rhinovirus,respiratorysyncytialvirus,parainfluenza andadenoviruscanalsopresentasInfluenza-likeIllness(ILI)whichmakestheclinicaldifferentiationofinfluenzafromotherpathogensdifficult.Collectionofappropriaterespiratorysamplesandtheapplicationofalaboratorydiagnostictestisrequiredtoestablishadefinitivediagnosis.Propercollection,storageandtransportofrespiratoryspecimensistheessentialfirststepforlaboratory detectionofinfluenzavirusinfections.Laboratoryconfirmationofinfluenzavirusfromthroat,nasalandnasopharyngealsecretionsortrachealaspirateorwashingsiscommonlyperformedusingdirectantigendetection,virusisolation,ordetection ofinfluenza-specificRNAbyreversetranscriptase-polymerasechainreaction(RT-PCR).VariousguidanceonthelaboratorytechniquesispublishedandupdatedbyWHO.(3) Rapidinfluenzadiagnostictests(RIDTs)areusedinclinicalsettings,buttheyhavelowersensitivitycomparedtoRT-PCRmethodsandtheirreliabilitydependslargelyontheconditionsunderwhichtheyareused.Treatment Patientswithuncomplicatedseasonalinfluenza:Patientsthatarenotfromahighriskgroupshouldbemanagedwithsymptomatictreatmentandareadvised,ifsymptomatic,tostayhomeinordertominimizetheriskofinfectingothersinthecommunity.Treatmentfocusesonrelieving symptomsofinfluenzasuchasfever.PatientsshouldmonitorthemselvestodetectiftheirconditiondeterioratesandseekmedicalattentionPatientsthatareknowntobeinagroupathighriskfordevelopingsevereorcomplicatedillness,(seeabove) shouldbetreatedwithantiviralsinadditiontosymptomatictreatmentassoonaspossible.Patientswithsevereorprogressiveclinicalillnessassociatedwithsuspectedorconfirmedinfluenzavirusinfection(i.e.clinicalsyndromesofpneumonia,sepsisorexacerbationofchronicunderlingdiseases)shouldbetreatedwith antiviraldrugassoonaspossible. Neuraminidaseinhibitors(i.e.oseltamivir)shouldbeprescribedassoonaspossible(ideally,within48hoursfollowingsymptomonset)tomaximizetherapeuticbenefits.Administrationofthedrugshouldalsobeconsideredinpatientspresentinglater inthecourseofillness.Treatmentisrecommendedforaminimumof5days,butcanbeextendeduntilthereissatisfactoryclinicalimprovement.Corticosteroidsshouldnotbeusedroutinely,unlessindicatedforotherreasons(eg:asthmaandotherspecificconditions);asithasbeenassociatedwithprolongedviralclearance,immunosuppressionleadingtobacterialorfungalsuperinfection. Allcurrentlycirculatinginfluenzavirusesareresistanttoadamantaneantiviraldrugs(suchasamantadineandrimantadine),andthesearethereforenotrecommendedformonotherapy.WHOGISRSmonitorsresistancetoantiviralsamongcirculatinginfluenzavirusestoprovidetimelyguidanceforantiviraluseinclinicalmanagementandpotentialchemoprophylaxis.PreventionThemosteffectivewaytopreventthediseaseisvaccination.Safeandeffectivevaccinesareavailableandhavebeenusedformorethan60years.Immunityfromvaccinationwanesovertimesoannualvaccinationisrecommendedtoprotect againstinfluenza.Injectedinactivatedinfluenzavaccinesaremostcommonlyusedthroughouttheworld. Amonghealthyadults,influenzavaccineprovidesprotection,evenwhencirculatingvirusesdonotexactlymatchthevaccineviruses.However,amongtheelderly,influenzavaccinationmaybelesseffectiveinpreventingillnessbutreducesseverityof diseaseandincidenceofcomplicationsanddeaths.Vaccinationisespeciallyimportantforpeopleathighriskofinfluenzacomplications,andforpeoplewholivewithorcareforthepeopleathighrisk. WHOrecommendsannualvaccinationfor:pregnantwomenatanystageofpregnancychildrenagedbetween6monthsto5yearselderlyindividuals(agedmorethan65years)individualswithchronicmedicalconditionshealth-careworkers.Influenzavaccineismosteffectivewhencirculatingvirusesarewell-matchedwithvirusescontainedinvaccines.Duetotheconstantevolvingnatureofinfluenzaviruses,theWHOGlobalInfluenzaSurveillanceandResponseSystem(GISRS)–asystem ofNationalInfluenzaCentresandWHOCollaboratingCentresaroundtheworld–continuouslymonitorstheinfluenzavirusescirculatinginhumansandupdatesthecompositionofinfluenzavaccinestwiceayear. Formanyyears,WHOhasupdateditsrecommendationonthecompositionofthevaccine(trivalent)thattargetsthe3mostrepresentativevirustypesincirculation(twosubtypesofinfluenzaAvirusesandoneinfluenzaBvirus).Startingwiththe2013–2014 northernhemisphereinfluenzaseason,a4thcomponentisrecommendedtosupportquadrivalentvaccinedevelopment.Quadrivalentvaccinesincludea2ndinfluenzaBvirusinadditiontothevirusesintrivalentvaccines,andareexpectedtoprovidewider protectionagainstinfluenzaBvirusinfections.Anumberofinactivatedinfluenzavaccinesandrecombinantinfluenzavaccinesareavailableininjectableform.Liveattenuatedinfluenzavaccineisavailableasanasalspray. Pre-exposureorpost-exposureprophylaxiswithantiviralsispossiblebutdependsonseveralfactorse.g.individualfactors,typeofexposure,andriskassociatedwiththeexposure. Apartfromvaccinationandantiviraltreatment,thepublichealthmanagementincludespersonalprotectivemeasureslike: RegularhandwashingwithproperdryingofthehandsGoodrespiratoryhygiene–coveringmouthandnosewhencoughingorsneezing,usingtissuesanddisposingofthemcorrectlyEarlyself-isolationofthosefeelingunwell,feverishandhavingothersymptomsofinfluenzaAvoidingclosecontactwithsickpeopleAvoidingtouchingone’seyes,noseormouthWHOresponseWHO,throughtheWHOGISRSsystem,incollaborationwithotherpartners,monitorsinfluenzaactivityglobally,recommendsseasonalinfluenzavaccinecompositionstwiceayearfortheNorthernandSouthernhemisphereinfluenzaseasons,guidescountries intropicalandsubtropicalareastochoosevaccineformulations(Northernhemispherevs.Southernhemisphere),tosupportdecisionsfortimingofvaccinationcampaigns,andtosupportMemberStatestodeveloppreventionandcontrolstrategies. WHOworkstostrengthennational,regionalandglobalinfluenzaresponsecapacitiesincludingdiagnostics,antiviralsusceptibilitymonitoring,diseasesurveillanceandoutbreakresponses,andtoincreasevaccinecoverageamonghighriskgroupsandprepare forthenextinfluenzapandemic. (1) EstimatesofUSinfluenza-associateddeathsmadeusingfourdifferentmethods.ThompsonWW,WeintraubE,DhankharP,ChengOY,BrammerL,MeltzerMI,etal.InfluenzaOtherRespiViruses.2009;3:37-49(2) Globalburdenofrespiratoryinfectionsduetoseasonalinfluenzainyoungchildren:asystematicreviewandmeta-analysis.NairH,AbdullahBrooksW,KatzMetal.Lancet2011;378:1917–3(3) WHOrecommendedsurveillancestandards,Secondedition. 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