outbreak investigation

• What is the baseline level of disease?

  The expected level of disease in a community
• What does sporadic mean in terms of disease occurrence?

  Occurs infrequently and irregularly
• What is an endemic disease?

  Constant presence of a disease in a population
• What characterizes a hyperendemic disease?

  Persistently high levels of disease occurrence
• What defines an epidemic?

  Sudden increase in disease cases above normal
• How is an outbreak similar to an epidemic?

  Both involve increased disease cases
• What is a cluster in disease terms?

  Aggregation of cases in place and time
• What is a pandemic?

  An epidemic spread over several countries
• What is the definition of an epidemic according to Last (1988)?

  Cases limited to a specified group during a short time
• What two conditions must be met for epidemics to occur?

  Agents and hosts must be present adequately
• What factors may trigger an epidemic?

  Increase in virulence, introduction of agent
• What is the primary goal of an outbreak investigation?

  Identify the source and guide intervention
• What are the reasons for investigating outbreaks?

  1. Prevention and Control
  2. Gain additional knowledge/research
  3. Training
  4. Public, political, or legal concerns
  5. Program considerations
• What is the goal when cases are continuing to occur in an outbreak?

  Prevent occurrence of additional cases
• What is the objective if an outbreak appears to be almost over?

  Prevent similar outbreaks in the future
• What factors influence the decision to investigate an outbreak?

  Source of illness, mode of transmission
• What knowledge is necessary to prepare for outbreak investigations?

  Epidemiologic characteristics and clinical symptoms
• What is the first step in an outbreak investigation?

  Verify the diagnosis and confirm the outbreak
• How can the existence of an epidemic be detected?

  Regular analysis of surveillance data
• What can initial investigations reveal?

  True outbreaks or sporadic unrelated cases
• What is a case definition in outbreak investigations?

  A uniform way to identify cases
• What are the three components of a case definition?

  Person, Place, and Time
• What is an epidemic curve?

  Graphical depiction of illness cases over time
• What does the shape of an epidemic curve reveal?

  The type of outbreak and its characteristics
• What characterizes a common source outbreak?

  People exposed to the same source
• What is a propagated epidemic?

  Spread from person to person
• What is the attack rate?

  Proportion of persons experiencing an acute event
• How is cumulative incidence calculated?

  New cases divided by population at risk
• What does the secondary attack rate measure?

  New cases among contacts of known patients
• What information can be obtained from an epidemic curve?

  Magnitude and time trend of the outbreak
• What do outliers in an outbreak represent?

  Cases not related to the main outbreak
• How can the incubation period be estimated using an epidemic curve?

  By analyzing the time between exposure and peak
• What should be done if a source of contamination is identified?

  Institute control measures immediately
• What are the aims of an outbreak investigation?

  Determine cause and prevent further spread
• What are the 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
  4. Do immediate control measures
  5. Formulate and test hypotheses
  6. Plan and execute additional studies
  7. Implement and evaluate control measures
  8. Communicate findings
• What factors affect the duration of an epidemic?

  • Number of susceptible persons exposed
  • Duration of exposure to the source
  • Minimum and maximum incubation periods
• What are the categories of cases in an outbreak?

  1. Confirmed: Symptoms, lab test, epidemiologic link
  2. Probable: Symptoms confirmed, no lab or link
  3. Suspected: Symptoms reported but not confirmed
• What are the types of common source outbreaks?

  1. Common Point Source
  2. Continuous Exposure
  3. Intermittent Exposure
• What are the characteristics of a propagated epidemic?

  • Spread from person to person
  • Can last longer than source outbreaks
  • May have multiple waves
• What are the examples of epidemic according to incubation period?

  • Hours: Acute food poisoning
  • Days: Salmonella, influenza
  • Weeks: Measles, hepatitis A
  • Months: Hepatitis B, rabies
  • Years: Radiation-induced leukemia