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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,

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Factors that affect disease dynamics and outbreaks

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  1. 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

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

  3. 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

  4. 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

  5. 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

  6. 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

  7. 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

  8. 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

  9. 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?

  10. 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

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

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