CORSO DI IGIENE

Scuoladi

Medicina

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Agenda

• Definitions• Burdenofinfectiousdiseases• Determinantsofinfectiousdiseases• Spreadofthediseases

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IENEInfectiousagents

allmicro-organismsormacro-organismscapableofproducinganinfectionoraninfectiousdisease• Virus• Bacteria• Fungus• Prion• protozoan

Barreto etal,JEpidemiol CommunityHealth.2006

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IENEInfectiousagents

• Agreatpartofourbodyiscolonizedbybacteria

• Afterashower,for1cm2 oftheskin,wecancollect100.000bacteria

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Classificationofbacteria

• PathogenBacteriumableincausingdiseaseinthehost• Commensalaparasiticorganismthatcausesnoharmtothehost

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Caracteristicsofapathogenbacterium

• Invasivity• Toxicity

Thegradeofexpressionofpathogenicity isnamedVirulence

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INA

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Commensal bacteria

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Commensal bacteria

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IENEInfectious disease

• illnesscausedbyaspecificinfectiousagentoritstoxicproduct

• IDresultsfromtransmissionoftheagentoritsproductsfromaninfectedperson,animal,orreservoirtoasusceptiblehost,eitherdirectly orindirectly throughanintermediateplantoranimalhost,vectororinanimateenvironment

Barreto etal,JEpidemiol CommunityHealth.2006

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Naturalhystoryofinfectiousdisease

Infection

Incubation

Clinicalevidenceofthedisease

death Convalescence

healing

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IENEContagiousdisease

Infectiousdiseasetrasmitted throughcontactwithillorcarrierpersons

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Infection

• theentranceanddevelopmentofaninfectiousagentinahumanoranimalbody,whetherornotitdevelopsintoadisease

• Thedetectionofthisstateinwhichtherearenosignsofarecognizedrelateddiseaseiscalledunapparentinfection

Barreto etal,JEpidemiol CommunityHealth.2006

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IENEContamination

Thepresence ofaninfectiousagentonabodysurface,onorinclothes,beddings,toys,surgicalinstrumentsordressing,orotherarticlesorsubstancesincludingwaterandfood

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Infestation

Lodgment,developmentandreproductionofartropodsorparasiticonthesurfaceofthebodyorintheclothing

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IENEVector ofinfection

Aninsectoranylivingcarrierthattransportsaninfectiousagentfromaninfectedpersonsoritswastestoasusceptibleindividualoritsfoo

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IENEVector ofinfection

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Reservoir ofinfection

• Anyperson,animal,plant,soilorsubstanceinwhichaninfectiousagentnormallylivesandmultiplies.

• Theinfectiousagentprimarilydependsonthereservoirforitssurvival.

• Itisfromthereservoirthattheinfectioussubstanceistransmittedtoahumanoranothersusceptiblehost

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IENETypes ofreservoirs

• Humansreservoirs– Case– Carriers

• Animalreservoirs• Nonlivingreservoirs

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Carriers

individualthathasthepathogenpresentbutisnotshowingthesignsandthesymptomsofthedisease• convalescent carriersalmonellosis• incubatory carriermeasles, meningococcal• healthy carrierrubella, mumps, hepatitis A, epstein barrvirus

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Reservoir ofinfection

Pathogen ReservoirMeasles Human subjectLegionella waterToxoplasma catMeningococcal HumansubjectRabies Dog,fox

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BURDEN OFINFECTIOUS DISEASES

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Burden ofinfectious diseases

Dyeetal,PhilosTransRSocLondBBiolSci.2014

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Burden ofinfectious diseases

Dyeetal,PhilosTransRSocLondBBiolSci.2014

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Burden ofinfectious diseases

Dyeetal,PhilosTransRSocLondBBiolSci.2014

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Burden ofinfectious diseases

Dyeetal,PhilosTransRSocLondBBiolSci.2014

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Burden ofinfectious diseases

Dyeetal,PhilosTransRSocLondBBiolSci.2014

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Thewaragainst infectious diseasehas not yet won

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Anewinfectious disease couldrapidly change lifeexpectancy

Source:WorldBankWorldDevelopmentIndicators,2004

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ThecaseofEbolavirus

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Also indeveloping countries there isfear ofinfectious diseases

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Also indeveloping countries there isfear ofinfectious diseases

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DETERMINANTS OFINFECTIOUSDISEASES

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IENEKoch’s Postulates

• Pathogenmustbepresentinallcasesofdisease

• Pathogenmustbeisolatedandgrowninlabinpureculture

• Pathogenfrompureculturesmustcausediseasewheninoculatedintohealthy,susceptiblelabanimal

• Samepathogenmustbeisolatedfromthediseasedlabanimal

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IENEKoch’s Postulates

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DIIG

IENEKoch’s Postulates

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Infectious disease model

disease

Host

PathogenEnvironment

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Determinants ofinfection

Virulence Bacterial/Viral

Load

Aspecific andspecificimmunity

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Opportunistic infections

infectionsthatoccurmorefrequentlyandaremoresevereinindividualswithweakenedimmunesystems,includingpeoplewithHIV

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Opportunistic infections

• Candidiasisofbronchi,trachea,esophagus,orlungs

• Invasivecervicalcancer• Invasivefungine infections• Cytomegalovirusdiseases(particularlyretinitis)

• Herpessimplex(HSV):chroniculcer(s)• Tuberculosis• Pneumocystis carinii pneumonia

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MODEOFTRASMISSION OFINFECTIOUS DISEASES

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Modeoftrasmission

Reservoir

Directtransmission

Droplet Aerosol

Skintoskin Sexualtransmission

Verticaltransmission

Indirecttransmission

Fomites Vectors

Foodandwater

Intermediatehosts

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Trasmission probability ratioTPR

• Measureoftherisktransmissionfrominfectedtosusceptibleindividualsduringcontact

• TPRdependsby– Typeofcontact– Infectiousagents– Infectionroutes– Infectionstrains

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TPR

TPR source hostp00 unimmunized unimmunizedp01 immunized unimmunizedp10 unimmunized immunizedp11 immunized immunized

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SPREADOFTHEDISEASE

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Spreadofinfectious disease

• Sporadic• Endemic

– Hyperendemic– holoendemic

• Epidemic/Outbreak• Pandemic• Cluster

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Sporadic

diseasethatoccursinfrequentlyandirregularlyinageographicarea

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Endemic

theongoing,usuallevelof,orconstantpresenceofadiseaseinagivenpopulation• hyperendemic: persistentlevelofactivitybeyondorabovetheexpectedprevalence

• holoendemic: adiseasethatishighlyprevalentinapopulationandiscommonlyacquiredearlyinlifeinmostallofthechildrenofthepopulation

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Epidemic

occurrenceofonespecificdiseaseinagrouppopulation,community,orgeographicalarea,inexcessoftheusuallevelofexpectancy

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Pandemic

epidemicthatiswidespreadacrossacountry,continent,orlargepopulace,possibleworldwide

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Cluster

aggregation ofcasesgroupedinplace andtime thataresuspectedtobegreaterthanthenumberexpected,eventhoughtheexpectednumbermaynotbeknown