JohnSnowandtheBroadStreetCholeraOutbreakof1854CholerareachedtheBritishIslesintheearly1830s,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.用心爱心专心ThispagelooksatSnow'stwomostfamousanalysiscasesthathelpedtoprovehishypothesisthatcholerainfectionsoccurredthroughdrinkingwater.TheBroadStreetOutbreak,1854ThisisthemostfamouspieceofdataanalysisperformedbyJohnSnow,andhispromptactionundoubtedlysavedmanylives.TheoutbreakoccurredintheSohoDistrictofLondon,inandaroundBroadStreet.JohnSnowreasonedthatifcholerawasspreadbyamistormiasma,astheprevailingtheoriessuggested,thenthecasesshouldbeuniformlydistributedalongthestreets.Toseeifthiswasthecase,heplottedeachcholeracaseonamap,similartotheoneontheleft.Healsoplottedhouseswithmultiplecases,whichthemodernmapontheleftdoesnotshow.Ascanbeseen,thecasesarenotuniformlydistributed,butinsteadaredistributedinatightclusteraroundawaterpumplocatedonBroadStreet(nowBroadwickStreet).Snowwenttothepumpandtookawatersample.Lookinginhismicroscope,hefoundthewatercontainedabacteriawhichhehadnotseenbefore.Althoughheguessedthesewereresponsible,thiswasbeforetheinfectiousmicrobeworkofPasteurandKoch.Hewentbacktothepumpandremovedthepumphandle.TheBroadStreetcholeraoutbreakstoppedalmostliterallyovernight.Notnotedonthemapwassomeotherevidencewhichhelpedtosupportthewaterpump用心爱心专心hypothesis.Alocalworkhousewasalmostuntouched(onlyfivecases),duetoitusingwaterfromitsownuncontaminatedwell.Themapalsoshowssomeoutliers.Snow'sinvestigationsshowedthatthesewereduetopeoplewhowouldpassthewell(eg.onthewaytowork)andtakedrink.ThemapabovewasproducedwithMicrosoft®MapPoint®.IfyouareinterestedinusingMicrosoftMapPoint,seetheMapping-Tools.ComwebsiteforallofyourMapPointconsultancyandprogrammingneeds.TheGrandExperiment,1853-54AlthoughJohnSnowismostfamousforhisanalysisoftheBroadStreetoutbreak,thisanalysismerelyconfirmedatheoryhehadbeendevelopingovertheprecedingyears.Oneofhisbiggesttestswaswhathecalledhis"GrandExperiment",andwascarriedoutthroughouttheoutbreakof1853-54.HecarefullyanalysedthecholeradeathsinLondon,correlatingthemwiththesourceofdrinkingwater.AswellashandpumpssuchasatBroadStreet,muchofLondon'spopulationreceivedmachine-pumpedwatersimilartowhatwehavetodaybutwithoutthetreatmentplants.Twocompaniessuppliedwaterlikethis.Duetonewlaws,theLambethCompanyhadstartedtotakeitswaterfromtheRiverThamesabout20milesup-streamofLondon,buttheSouthwarkandVauxhallWaterCompanywasstilltakingitswaterfromlocalwellsandtheThamesinCentralLondon.ThisprovidedaperfectcomparisonforSnow.Snow'sfinalsummarytable:No.ofhousesDeathsfromcholeraDeaths/10,000housesSouthwarkandVauxhallCompany40,0461,263315用心爱心专心LambethCompany26,1079837RestofLondon256,4231,42259Hence,Snowshowedastrongcorrelationbetweenthecholeradeathrateandthewatersource.Thedataalsoshowsthatawatersourceup-riveroftheLondonwasthesafestoption,whilsttakingwaterdirectlyfromtheThamesinCentralLondonwasmoredangerousthanotherlocalwatersourcescombined.用心爱心专心
