Outbreak Outbreak InvestigationInvestigation

ObjectivesObjectives

Determine if an outbreak is occurringDetermine if an outbreak is occurring Characterise the outbreakCharacterise the outbreak Identify additional casesIdentify additional cases Identify causative agentIdentify causative agent Identify the source Identify the source Initiate steps to terminate transmissionInitiate steps to terminate transmission Learn for the futureLearn for the future

Surveillance for diseaseSurveillance for disease

Certain infectious diseases pose Certain infectious diseases pose significant threats to the health of the significant threats to the health of the publicpublic

It is important that public health know It is important that public health know about themabout them

States, federal and international health States, federal and international health authorities develop lists of reportable authorities develop lists of reportable disease.disease.

SurveillanceSurveillance

Physicians, hospitals and clinical laboratories Physicians, hospitals and clinical laboratories are required to report, usually within a specified are required to report, usually within a specified time periodtime period

Serious diseases are often categorized Serious diseases are often categorized separatelyseparately

Basic functions of communicable disease Basic functions of communicable disease control at the state and local levels is the control at the state and local levels is the gathering and analysis of reportable disease gathering and analysis of reportable disease datadata

Examples of Reportable Examples of Reportable Diseases in MichiganDiseases in Michigan

Enteric diseasesEnteric diseases Salmonellosis, shigellosis, Campylbacter, hepatitis Salmonellosis, shigellosis, Campylbacter, hepatitis

AA Sexually Transmitted DiseasesSexually Transmitted Diseases

Syphilis, gonorrhea, HIVSyphilis, gonorrhea, HIV CNS diseasesCNS diseases

Bacterial and viral meningitis, Arboviral – WNV, EEEBacterial and viral meningitis, Arboviral – WNV, EEE Vaccine Preventable DiseasesVaccine Preventable Diseases

Measles, mumps, diphtheria, polio, hepatitis BMeasles, mumps, diphtheria, polio, hepatitis B

Collection and analysis of Collection and analysis of datadata

LHD receives reportsLHD receives reports LHD logs and reviews dataLHD logs and reviews data

Number of cases within a specific time period e.g a Number of cases within a specific time period e.g a weekweek

Geographic distribution of casesGeographic distribution of cases Determination if the cases need further investigationDetermination if the cases need further investigation

LHD send s reports to MDCH via LHDSurv LHD send s reports to MDCH via LHDSurv (soon to be replaced by MDSS)(soon to be replaced by MDSS)

MDCH sends reports to CDC via NETSSMDCH sends reports to CDC via NETSS

Data analysisData analysis

Need to know background levelNeed to know background level Track weekly occurrence of disease over a Track weekly occurrence of disease over a

number of years to establish an average number of years to establish an average number of cases per week for that particular number of cases per week for that particular weekweek

Need to determine when the number of Need to determine when the number of cases is above the backgroundcases is above the background

Establish when an Establish when an outbreak is occurringoutbreak is occurring

For some diseases, a single case is an For some diseases, a single case is an outbreak e.g measles, smallpoxoutbreak e.g measles, smallpox

In others, use the background as a threshold, In others, use the background as a threshold, but take into account other variables but take into account other variables e.g. is the gender or age frequency similar to e.g. is the gender or age frequency similar to

previous years, previous years, are the cases clustered geographicallyare the cases clustered geographically

Sometimes the illness is reported before Sometimes the illness is reported before a disease is identifieda disease is identified Many calls from physicians and the public Many calls from physicians and the public

about persons becoming ill with diarrhea, about persons becoming ill with diarrhea, vomitingvomiting

Using symptoms try to ascertain the likely Using symptoms try to ascertain the likely diseasedisease

Get specimens to send to the laboratory Get specimens to send to the laboratory if not already obtainedif not already obtained

InvestigationInvestigation

Characterize the data that you haveCharacterize the data that you have Try to identify other similar cases Try to identify other similar cases

occurringoccurring How would you do this? How would you do this?

Fax to ERsFax to ERs Notices on electronic boards Notices on electronic boards

Case definitionCase definition

What would you need in a case definitionWhat would you need in a case definition TimeTime PlacePlace SymptomsSymptoms E.g. All persons who experienced vomiting, E.g. All persons who experienced vomiting,

diarrhea, nausea or abdominal cramping diarrhea, nausea or abdominal cramping and who ate at Joe’s Greasy Spoon and who ate at Joe’s Greasy Spoon between Dec 10 and Dec 14.between Dec 10 and Dec 14.

Data AnalysisData Analysis

Determine which cases fit the case definitionDetermine which cases fit the case definition Analyse by variablesAnalyse by variables

AgeAge GenderGender RaceRace GeographyGeography Risk factorRisk factor

Food Food DrinkDrink Behavior e.g. smoking, outdoor activity, attends day careBehavior e.g. smoking, outdoor activity, attends day care

Data analysisData analysis

FrequenciesFrequencies Incubation periodsIncubation periods Laboratory testsLaboratory tests Epidemic curveEpidemic curve Attack ratesAttack rates

By personBy person By placeBy place By risk factorBy risk factor

Hypothesis Hypothesis

Using the data analysis, formulate Using the data analysis, formulate hypotheseshypotheses

Select the hypothesis which fits the Select the hypothesis which fits the picturepicture

Hypothesis should addressHypothesis should address Source of the diseaseSource of the disease Etiologic agentEtiologic agent Method of transmissionMethod of transmission Control methodsControl methods

Hypothesis generationHypothesis generation

Hypotheses can be generated at any Hypotheses can be generated at any time during the investigation, and refined time during the investigation, and refined as more data becomes available. But as more data becomes available. But beware of making false assumptionsbeware of making false assumptions

But don’t leave it too late, as hypothesis But don’t leave it too late, as hypothesis generation should lead to control generation should lead to control measuresmeasures

Hypothesis testingHypothesis testing

Laboratory results can confirm the Laboratory results can confirm the etiologic agentetiologic agent

Prevent further consumption of Prevent further consumption of implicated food can confirm the implicated food can confirm the transmission/sourcetransmission/source

Data analysis – Data analysis – Case – control study using matched or Case – control study using matched or

unmatched controls.unmatched controls.

Control methodsControl methods

Initiate control methods based upon Initiate control methods based upon hypothesishypothesis

Report of findingsReport of findings

So others can learn from our experienceSo others can learn from our experience