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  • Public health notes
  • Read this: wikipedia:Outbreak
  • Map the spread
  • Case definition
  • Compare it to background rate of disease
  • Outbreak = 'more cases of an infectious disease than expected in a given area or among a specific group of people over a particular period of time
    • Person, place, time

'expected' rate

  • Notifiable disease surveillance data
  • Hospital discharge data
  • Mortality statistics
  • Other disease registries
  • National/state health surveys
  • Published literature and epidemiology studies
  • Google "national notifiable disease surveillance system"


How to know an outbreak is occurring?

  • Alerted to by a amember of the medical community
    • Publi
    • Media report
    • Notifications data
    • By looking for them

If we have an increase in cases, what's the reason?

  • Seasonal variation
  • Better diagnosis
  • Change in age distribution/population characteristics
  • Random variation
  • Change in the size of the population
  • Changes in lab testing
  • Contamination in specimens
  • Change in reporting

Why investigate an outbreak

  • More dangerous/virulent strain
  • Prevention of transmission
  • To describe the outbreak (magnitude, source, etc)
  • Understand current disease epi
  • Evaluate existing prevention strategies
  • INform future public health
  • Inform government

Investigation involves

  • Epi investgation
  • Environmental investigation
  • Interaction with public/media

Ten steps in outbreak investigation

  1. Determine existence of outbreak
  2. Confirm the diagnosis
  3. Define a case and count cases
  4. Orient the data in terms of time, place and person
  5. Determine who is at risk of becoming ill
  6. Develop hypothesis
  7. Evaluation hypotheses
  8. Perform additional studies
  9. Execute control and prevention measures
  10. Communicate findings

Case study - salmonella

  • 2007, an increase in Salmonella infections was noted
  • Probable S. enterica variant Java outbreak centred on a single local government area
  • A total of 75 cases
  • Causes gastroenteritis symptoms lasting 7 days
  • Overseas acquired
  • Salmonellosis is a notifiable disease in NSW - PHU NOTICES AN INCREASE IN CASES
  1. confirmed case = lab identified OR clinical + epi data
  2. probable case = clinically identified AND laboratory suggestive evidence
  3. suspected case = contact, not fitting clinical syndrome
  • only confirmed cases are reported for salm

Case study - measles

  • Reporting
    • Both confirmed cases and probably cases must be notified
  • Clinically suspected cases should also be notified

Time place and person orientation

  • Epi curve = cases vs time
    • Person-person spread = a few cases early, then later on there is an explosion
    • Point source (e.g. food) = a blob around the incubation period
    • Common source (intermittent e.g. water) - background dribble over time
      • e.g. the graph on the paper is common source
  • in salmonella, you want to find the source e.g. case control (compare exposure of diseased people to the people who aren't disease)
  • cohort
    • group of people defined and measured for presence or absence of exposure (exposure status defined before disease outcome known)
    • can measure incidence
    • follow up over time
  • case -control
    • select subjects based on presence or absence of disease and then compare exposure
    • can measure odds
  • they did the salmonella cohort study using a telephone survey
  • you need a case definition and a control definition (inclusion/exclusion criteria)
  • intervention possibilities: contact tractin? isolation? education?
  • odds ratio (case control study) = ad/bc
    • OR > 1 = exposure is harmful
    • OR < 1 = exposure is protective
  • relative risk (cohort study)

What prevention strategies should be carried out:

  • Among the families of ill children
  • In the community
  • By councils

Replace contaminated sand in sandpits

  • Playground options
    • sand
    • bark (less likely to be ingested, smaller surface area to volume)
    • rubberised surface
  • signage and media coverage about hygiene

Communicate findings

  • Document actions
  • Program planning
  • Policy
  • Medical/legal issues
  • Improve quality of investigation
  • Teaching tool
  • Write a report
  • Consider submission for publication