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Factors that affect disease dynamics and outbreaks. a recent increase in amount or virulence of the agent, recent introduction of the agent into settings where it has not been before, enhanced mode of transmission so that more susceptible individuals are exposed,

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Factors that affect disease dynamics and outbreaks


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factors that affect disease dynamics and outbreaks
Factors that affect disease dynamics and outbreaks
  • a recent increase in amount or virulence of the agent,
  • recent introduction of the agent into settings where it has not been before,
  • enhanced mode of transmission so that more susceptible individuals are exposed,
  • an environment that is conducive to interaction between the host and the agent,
  • a change in the host susceptibility to agents,
  • factors that increase host exposure or or involve introduction through new portals of entry
slide2

Disease Levels and Patterns

    • Levels of disease
    • ·        Epidemic
    • ·        Outbreak
    • ·        Cluster
    • ·        Endemic
    • ·        Pandemic
    • Patterns of disease occurrence:
    • common source
      • point
      • intermittent
      • continuous
    • Propagated
    • Mixed
    • Other
slide3

Susceptibility to the effect (s) of agent(s):

  • susceptible, immune, infected
  • Spectrum of response to exposure:
  • sub-clinical
  • clinical
  • ·   mild
  • ·   severe
  • Environment
    • Surrounding conditions/influences not part of agent or host
    • Components: physical, climatologic, biologic, social, economic
slide4

Transmission

      • ·        Agent
      • ·        Source
      • ·        Transmissibility of the agent
      • ·        Susceptibility of exposed hosts
  • Modes of Spread
      • Direct contact
      • intimate contact
  • oral, respiratory, mucus membranes,
  • blood
      • Indirect contact
      • vehicles
      • vectors
slide5

Epidemiologic approaches to outbreak investigation:

    • ·Determines prevalence and incidences of disease in well-defined populations.
    • ·Makes inferences.
  • Epidemiologic approach covers:
    • Factors related to host
    • Exposure
    • Susceptibility
    • Factors related to agent(s):
    • Modes of transmission.
    • Factors related to vectorsand the Environment.
  • Epidemiologic studies:
    • Non-experimental (observational)
    • Cohort
    • Case-control
    • Cross-sectional
    • Ecological
    • Experimental
    • Clinical trials
    • Field trials
    • Community intervention trials
slide6
Morbidity and mortality rates:

Attack rate Prevalence  Time   Temporal relation between

exposure and occurrence   

How to graph time data    Number of cases over time

    Rates over time

special features
Special Features

i.Examining your graph

ii.    Epidemic curve

iii.    Point sources epidemics

iv.   Person to person

  v.   Intermittent or continuing common source

 vi.   Information on place

vii.   How to examine place

viii.  Person

ix.   Attribute categories

  x.   Examination of person data

 xi.   Interpretation of person data

reasons and standards for epidemiologic investigations
Reasons and standards for epidemiologic investigations:

Operational aspects of epidemiologic investigations

i.   Legal considerations in a Field investigation

ii.  Investigation in food catering facilities

iii. Investigation in child care facilities

iv. Epidemiologic investigation in international

settings

v.  Laboratory support for the epidemiologic

investigation in the field

vi. Dealing with the public and the media

response and responsibilities
Response and responsibilities:

2. The

i.  To control and prevent further disease

                     ii.      To provide agreed upon or statutorily mandate services

                     iii.      To derive more information about interaction between the human

host, the foodborne agent, and the environment

                     iv.      To strengthen surveillance at eh local level through assessment of

its quality and by direct and personal contact or to determine the

need to establish a new surveillance system

                      v.      To provide training opportunities in epidemiology

                     vi.      What resources, including personnel, will be available locally?

                     vii.     What resources will be provided by the visiting team?

                     viii.    Who will direct the day-to-day investigation?

                     ix.      Who will provide the overall supervision and ultimately be

responsible for the investigation?

                      x.      How will the data be shared and who will be responsible for their

analysis?

                     xi.      Will a report of the findings be written?

ten steps of field investigation
Ten steps of field investigation:

·

i.Determine the existence of the epidemic

                      ii.      Confirm the diagnosis

                     iii.      Define a case and count cases

                     iv.      Orient the data in term of time, place, and person

                      v.      Determine who is at risk of becoming ill

                     vi.      Develop a hypothesis explaining the specific

exposure that caused disease and test this

hypothesis by appropriate statistical methods

                     vii.     Compare the hypothesis with the established

facts

                     viii.    Plan a more systemic study

                     ix.      Prepare a written report

x. Execute control and preventive measures

slide13

Management

      • Log decisions
      • Accuracy
      • Communication
      • Kiss (keep it simple, Stupid)
      • Ongoing writing
      • Filing
      • Friendship
      • Departure
  • 9. Reports