Outbreak Investigation

• Baseline


  The amount of a disease that is usually present in a community; the observed but not necessarily the desired level; regarded as the expected level of disease
• Sporadic


  A disease that occurs infrequently and irregularly
• Endemic


  The constant presence and/or usual prevalence of a disease or infectious agent in a population within a geographic area
• Hyperendemic


  The persistently high levels of disease occurrence in a particular place
• Epidemic


  An increase, often sudden, in the number of cases of a disease above what is normally expected in that population in that area
• Outbreak


  Similar to an epidemic but is often used for a more limited geographic area
• Cluster


  An aggregation of cases grouped in place and time that are suspected to be greater than the number expected, even though the expected number may be unknown
• Pandemic


  An epidemic that has spread over several countries or continents, usually affecting a large number of people
• Aims of outbreak investigation


  • Assess the range and extent of an outbreak
  • Identify new syndromes, new cases, or new diseases
  • Train epidemiologists
  • Assess effectiveness of current prevention strategies
  • Determine the cause of the outbreak
  • Prevent further spread of the outbreak
  • Educate responsible individuals in the prevention of similar outbreak in the future
• Reasons for investigating outbreaks


  • Prevention and control
  • Gain additional knowledge/research
  • Training
  • Public, political, or legal concerns
  • Program considerations
• Steps in an outbreak investigation


  1. Verify the diagnosis and confirm the outbreak

  2. Define a case and conduct case finding

  3. Tabulate and orient data: time, place, person

  4. Do immediate control measures after analyzing the data

  5. Formulate and test hypothesis

  6. Plan and execute additional studies

  7. Implement and evaluate control measures

  8. Communicate findings
• Preparation for field work


  • Investigation
  • Administration
  • Consultation
• Knowledge necessary to prepare for outbreak investigations


  • Various types of etiologic agents and the resultant disease
  • Epidemiologic characteristics of outbreaks associated with different etiologic agents or resultant diseases
  • Clinical symptoms of resultant diseases
  • Environmental and food sanitation practices
  • Sources of exposure which are vulnerable to contamination with an infectious or chemical agent
  • Laboratory test available to determine causative agents
• With proper chain of authority involved within the process, you should not bypass any protocols or systematic process (so not to create any confusion or misinformation)
• Knowledge necessary to prepare for outbreak investigations

  • Various types of etiologic agents and the resultant disease
  • Epidemiologic characteristics of outbreaks associated with different etiologic agents or resultant diseases
  • Clinical symptoms of resultant diseases
  • Environmental and food sanitation practices
  • Sources of exposure which are vulnerable to contamination with an infectious or chemical agent
  • Laboratory test available to determine causative agents
• MedTechs


  One of the best professionals (qualified individuals) to conduct an investigation
• MedTechs are equipped with necessary knowledge about different agents causing diseases
• One advantage with our profession (MedTechs) is that we can determine the causative presence or absence of disease
• Steps in outbreak investigation


  1. Verify the diagnosis and confirm the outbreak

  2. Establish the existence of an outbreak
• Verify the diagnosis and confirm the outbreak


  • Confirm laboratory
  • Rule out misdiagnoses or laboratory error
• Ways to gain knowledge/awareness of an existence of an epidemic


  • Regular analysis of surveillance data - detect unusual patterns of disease occurrence
  • Calls from a health care provider or a citizen who knows of several cases
  • Media reports
• Initial investigation may turn out to be


  • True outbreaks with a common cause
  • Sporadic and unrelated cases of the same disease
  • Unrelated cases of similar but unrelated disease (i.e.,without a common cause)
• Comparison of the observed number of cases with the expected number


  1. The number of cases from the previous few weeks or months

  2. The number of cases from a comparable period during the previous few years
• Source of data to establish 'expected number cases'


  • Health department surveillance data if disease is a notifiable disease
  • Hospitals discharge records, mortality statistics, cancer or registries if disease is non-notifiable
  • Apply rates from neighboring areas or conduct an informal survey among local physicians
  • Conduct survey of the community to establish background level of the disease
• Factors which could explain excess cases

  • Changes in local reporting procedures
  • Changes in the case definition
  • Increased interest because of local or national awareness
  • Improvements in diagnostic procedures
  • Sudden increases in size of population in particular areas
• Factors influencing decision regarding investigation of the outbreak


  • Severity of the illness
  • The potential for spread
  • Political consideration
  • Public relations
  • Availability of resources, etc.
• Define a case and conduct case finding

  1. Identifying who will be those individuals to be included on your cases

  2. To identify individuals who have the disease
• Case


  Individuals who have the disease
• Develop a specific case definition


  1. Using symptoms or laboratory results

  2. Using time period

  3. Using location
• Case definition


  • Allows a simple, uniform way to identify cases
  • Standardizes the investigation
  • Is unique to outbreak but is based on objective criteria
  • Always includes: PERSON, PLACE, AND TIME
• Categories of cases


  • Confirmed
  • Probable
  • Suspected
• Tabulate and orient data


  1. Create a line listing of identified cases

  2. Create a spot map

  3. Create an epidemic curve
• Line listing


  Using the three variables: person, place, time to search for additional cases
• Spot map


  A graphical depiction of the location of cases
• Epidemic curve


  A graphical depiction of the number of cases of illness by the date of illness onset
• Types of epidemic curves


  • Common source (point, continuous, intermittent)
  • Propagated
  • Mixed
• Common source outbreak


  People who harbor the disease are exposed continuously or intermittently to a harmful source
• Common point source outbreak


  Cases were all exposed to the same source during a brief period of calendar time
• Continuous exposure outbreak


  Exposure duration is prolonged
• Propagated epidemic


  • Spread from person-to-person
  • Disease agent may replicate in a susceptible host as part of the transmission cycle
  • May have multiple waves