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Outbreak Investigation

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Certain infectious diseases pose significant threats to the health of the public. It is important that public health know about them ... – PowerPoint PPT presentation

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Title: Outbreak Investigation


1
Outbreak Investigation
2
Objectives
  • Determine if an outbreak is occurring
  • Characterise the outbreak
  • Identify additional cases
  • Identify causative agent
  • Identify the source
  • Initiate steps to terminate transmission
  • Learn for the future

3
Surveillance for disease
  • Certain infectious diseases pose significant
    threats to the health of the public
  • It is important that public health know about
    them
  • States, federal and international health
    authorities develop lists of reportable disease.

4
Surveillance
  • Physicians, hospitals and clinical laboratories
    are required to report, usually within a
    specified time period
  • Serious diseases are often categorized separately
  • Basic functions of communicable disease control
    at the state and local levels is the gathering
    and analysis of reportable disease data

5
Examples of Reportable Diseases in Michigan
  • Enteric diseases
  • Salmonellosis, shigellosis, Campylbacter,
    hepatitis A
  • Sexually Transmitted Diseases
  • Syphilis, gonorrhea, HIV
  • CNS diseases
  • Bacterial and viral meningitis, Arboviral WNV,
    EEE
  • Vaccine Preventable Diseases
  • Measles, mumps, diphtheria, polio, hepatitis B

6
Collection and analysis of data
  • LHD receives reports
  • LHD logs and reviews data
  • Number of cases within a specific time period e.g
    a week
  • Geographic distribution of cases
  • Determination if the cases need further
    investigation
  • LHD send s reports to MDCH via LHDSurv (soon to
    be replaced by MDSS)
  • MDCH sends reports to CDC via NETSS

7
Data analysis
  • Need to know background level
  • Track weekly occurrence of disease over a number
    of years to establish an average number of cases
    per week for that particular week
  • Need to determine when the number of cases is
    above the background

8
Establish when an outbreak is occurring
  • For some diseases, a single case is an outbreak
    e.g measles, smallpox
  • In others, use the background as a threshold, but
    take into account other variables
  • e.g. is the gender or age frequency similar to
    previous years,
  • are the cases clustered geographically

9
  • Sometimes the illness is reported before a
    disease is identified
  • Many calls from physicians and the public about
    persons becoming ill with diarrhea, vomiting
  • Using symptoms try to ascertain the likely
    disease
  • Get specimens to send to the laboratory if not
    already obtained

10
Investigation
  • Characterize the data that you have
  • Try to identify other similar cases occurring
  • How would you do this?
  • Fax to ERs
  • Notices on electronic boards

11
Case definition
  • What would you need in a case definition
  • Time
  • Place
  • Symptoms
  • E.g. All persons who experienced vomiting,
    diarrhea, nausea or abdominal cramping and who
    ate at Joes Greasy Spoon between Dec 10 and Dec
    14.

12
Data Analysis
  • Determine which cases fit the case definition
  • Analyse by variables
  • Age
  • Gender
  • Race
  • Geography
  • Risk factor
  • Food
  • Drink
  • Behavior e.g. smoking, outdoor activity, attends
    day care

13
Data analysis
  • Frequencies
  • Incubation periods
  • Laboratory tests
  • Epidemic curve
  • Attack rates
  • By person
  • By place
  • By risk factor

14
Hypothesis
  • Using the data analysis, formulate hypotheses
  • Select the hypothesis which fits the picture
  • Hypothesis should address
  • Source of the disease
  • Etiologic agent
  • Method of transmission
  • Control methods

15
Hypothesis generation
  • Hypotheses can be generated at any time during
    the investigation, and refined as more data
    becomes available. But beware of making false
    assumptions
  • But dont leave it too late, as hypothesis
    generation should lead to control measures

16
Hypothesis testing
  • Laboratory results can confirm the etiologic
    agent
  • Prevent further consumption of implicated food
    can confirm the transmission/source
  • Data analysis
  • Case control study using matched or unmatched
    controls.

17
Control methods
  • Initiate control methods based upon hypothesis

18
Report of findings
  • So others can learn from our experience
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