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JohnSnowandtheBroadStreetCholeraOutbreakof1854.doc

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JohnSnowandtheBroadStreetCholeraOutbreakof1854 CholerareachedtheBritishIslesintheearly1830s,andoutbreakswouldcontinueforthenextfiftyyears.Today,itiswellknownthatcholeraiscausedbythebacteriaVibriacholeraeandisusuallyspreadinpoordrinkingwater.Earlytheoriesblamedtheinfectiononmistsand'miasmas',whichledtomanyoftheearlyattemptstocontrolcholerafailing.Inrealitythepoorsanitaryconditionsofacity'swatersupplywasresponsible.EarlyVictoriancitiesalsoincludedcowshedsmixedinamongstthehouses.Thesecombinedwithpoorhandlingofhumansewage(oftenmerelyaholeintheground)ledtoarapidcontaminationofthedrinkingwater.Indeed,thefamousBroadStreetwaterpump(seebelow)wasashallowwaterpumpthatpumpedwaterfromthecontaminatedwatertable. Inthe1850s,JohnSnowperformedpioneeringdataanalysistoprovehishypothesisthatcholerawasspreadinthedrinkingwater.Thisanalysisifperformedtoday,wouldcomeundertherealmsofGIS(GeographicInformationSystems)andDataMining.SomehaveclaimedhisBroadStreetmapasbeingthefirstexampleofGIS,eventhoughitwasperformedwithapenandpaper.Althoughthisisanexaggeration,theBroadStreetmapitisanexcellentexampleofthepowerofmapstoclearlydemonstraterelationshipsincomplexscenarios.Snow'sworkwiththeLondoncholeraoutbreaksofthe1850s,isoftencitedasthebeginningofmodernepidemiology. Unfortunatelywordofthispioneeringepidemiologywasslowtospread,andtheLondoncholeraoutbreakswouldcontinueintothe1880swhenalloftheshallowwater-pumpswerefinallydecommissioned. ThispagelooksatSnow'stwomostfamousanalysiscasesthathelpedtoprovehishypothesisthatcholerainfectionsoccurredthroughdrinkingwater. TheBroadStreetOutbreak,1854 ThisisthemostfamouspieceofdataanalysisperformedbyJohnSnow,andhispromptactionundoubtedlysavedmanylives.TheoutbreakoccurredintheSohoDistrictofLondon,inandaroundBroadStreet. JohnSnowreasonedthatifcholerawasspreadbyamistormiasma,astheprevailingtheoriessuggested,thenthecasesshouldbeuniformlydistributedalongthestreets.Toseeifthiswasthecase,heplottedeachcholeracaseonamap,similartotheoneontheleft.Healsoplottedhouseswithmult