Diesease Detectives: L1 Steps for Outbreak Investigation

Outbreak Investigation

A structured, step-by-step process of gathering and studying health data to stop an active disease outbreak and prevent future ones

Step 1:

Prepare for Field Work

Step 2:

Establish the Existence of an Outbreak

Cluster

An aggregation or group of disease cases in a given location and time period that is not automatically an outbreak

Endemic

The routine, expected presence or level of a disease in a given population

Outbreak

The occurrence of more disease cases than expected in a specific population, place, and time, where the cases are presumed to be related

Epidemic

An outbreak that spreads across a wider geographic area

Surveillance

Routine local health data collection used to establish expected baseline disease levels and determine whether active case counts exceed expected numbers

Step 3

Verify the Diagnosis

Verify the Diagnosis: Frequency Distributions

Summarizing case data by variables such as date of onset, age, and gender to organize initial findings

Verify the Diagnosis: Verification Process

Reviewing clinical symptoms and laboratory techniques to rule out lab error, and interviewing cases to spot shared traits

Step 4

Identify and Define Cases

Identify and Define Cases: Case Definition

Setting standard criteria based on person, place, and time to systematically classify individuals as suspected, probable, or confirmed cases

★ (5) Step

Find Cases Systematically and Record Information

Find Cases Systematically and Record Information: Data Collection

Actively gathering case details across health facilities

Types of Information Collected: Identifying Information

Name, address, phone number

Types of Information Collected: Demographic Information

Age, race, sex

Types of Information Collected: Clinical Information

Signs, symptoms, date of onset, duration

Types of Information Collected: Risk Factor Information

Specific exposures

Types of Information Collected: Reporter Information

Source of the report

Step 5:

Perform Descriptive Epidemiology

Descriptive Epidemiology

Summarizing case data by demographic variables to identify patterns across population, place, and time, determine populations at risk, and generate hypothesis clues

Time (Epidemic Curves)

A graph plotting case counts by date of onset or sample collection to show transmission modes and incubation periods

Place (Spot Maps)

Visual maps marking case locations to reveal spatial patterns

Person Variables: Host Characteristics

Demographic traits of an individual such as age, race, sex, and medical status

Personal Variable: Host Factors

Specific host characteristics that directly affect a peron’s susceptibility to a disease

Personal Variables: Exposures

Activities, occupations, habits or behaviors that bring a host into contact with a disease source

Step 6:

Develop a Hypothesis

Hypothesis Focus

Proposing testable causes involving the agent, mode of transmission or primary exposure

Disease Frameworks:

Reservoir, mode of transmission, vehicles, risk factors

Disease Frameworks: Reservoir

The natural environment or living organisms where a pathogen normally lives and multiples

Disease Frameworks: Mode of Transmission

The pathway or method by which an agent travels from a reservoir to a host

Disease Frameworks: Vehicles

Non-living items that convery an infectious agent

Disease Frameworks: Risk Factors

Specific traits or conditions that increase a host’s likelihood of aquiring a disease

Step 7:

Evaluate Hypothesis

Analytical Epidemiology

using study designs to evaluate whether a true positive association exists between exposure and disease and whether that link is statistically significant

Observational Study Types:

Cohort study, Case control study

Relative Risk

How many times more likely is the exposed group to develop the disease compared to the unexposed group?

Observational Study Types: Cohort Study

observation study tracking groups from exposure status to disease status by measuring relative risk

Cohort Study: Prospective

tracking healthy patients to who catches the disease

Cohort Study: Retrospective

looking at records of exposure before the outcome

Odds Ratio

What are the odds that a person with the disease was exposed, compared to the odds that a person without the disease was exposed

Observational Study Types: Case Control study

observational study comparing cases to controls (healthy) and looking from disease status to exposure status measured by odds ratio

Statistcal Significance Measures: Confidence Interval

A range that provides the margin of error around a sample estimate

Statistcal Significance Measures: Z-test & T-test

Statistical tests used to determine if an observed sample value is significantly difference from an expected baseline value

Step 8

Re-evaluate and Refine Hypotheses

★ (10) Step

Compare & Reconcile w Lab and/or Environmental Studies

Compare & Reconcile w Lab and/or Environmental Studies: Laboratory Studies

testing used to conform analytical epidemiology findings, often considered necessary to close the case

Compare & Reconcile w Lab and/or Environmental Studies: Environmental Studies

physical inspections of environmental sites to explain how contamination first occured

Step 9

Implement Control and Prevention Measures

Implement Control and Prevention Measures: Chain of Infection

taking targeted public health actions to break transmission links

Chain of Infection

Infectious Agent —> Reservoir —> Portal of Exit —> Mode of Transmission —> Portal of entry —> Susceptible Host

★ (12) Step

Initiate or Maintain Surveillance

Initiate or Maintain Surveillance: Ongoing Monitoring

Continusouly tracking the rate and location of new cases to confirm whether control interventions are working and to verify if the outbreak is spread outside the intervention area

Step 10

Communicate Findings

Communicate Findings: Types

Oral briefing, written report