Feldmand. Module 6 - Outbreak investigation Flashcards
What is an outbreak?
- More cases of a particular disease than expected in a given area, or among a specific population, over a particular period of time
- The number of expected cases varies
Why investigate outbreaks?
• Protect the community’s health
– Remove the source of infection
– Provide prevention guidance
– Address concerns in the community
• Increased knowledge base
– Completing the clinical picture
– Identify new etiologic agents
– Identify new routes of transmission
Steps in an Outbreak Investigation
- Prepare for field work
- Establish the existence of an outbreak
- Verify the diagnosis
- Define and identify cases
- Describe and orient the data in terms of time, place, and subject
- Develop hypotheses
- Evaluate hypotheses
- Refine hypotheses and carry out additional studies
- Implement control and prevention measures
- Communicate findings
- Prepare for field work
An Outbreak in the Clinic…
• May be limited in scope and impact • Preparation includes – Coordination with clinic staff – Data collection equipment assembled: • Computer • Paper • Pencil • Calculator – Records pulled
- Prepare for field work
An Outbreak in the Community…
• Notification of people who “need to know” • Coordination with investigation partners • Assembly of equipment – Data collection – Communications – Clothing – Laboratory • Travel preparation
- Prepare for field work
Probable Partners
- Clinicians
- Epidemiologists
- Laboratory scientists
- Environmental scientists
- Infection control practitioners
- Decision makers
- Communications experts
- Law enforcement?
- Others depending on context
- Establish the existence of an outbreak
• Need to determine (quickly) if current rate exceeds background
• Many infectious diseases are reportable
• Beware of artifactual changes
– Change in reporting practices
– New diagnostic tests
– Increased clinician awareness
- In the clinic, pull records for same period last year and compare
- Survey clinicians
- Acquire absentee records
- May need to proceed with investigation because of local pressures even if unsure outbreak exists
- Verify the diagnosis
Confirm the clinical diagnosis
• Confirm by standard laboratory techniques
• If possible, visit the laboratory and verify in person
• Do not need confirmation on every patient
• Sometimes new agent
– Proceed despite lack of diagnosis
- Define and identify cases
Case Definition
• Imperative to be systematic
• Consists of clinical criteria and other criteria to specify subject, place, and time
• Use simplest and most objective criteria
• Apply definition equally and without bias
• Degrees of certainty may be included (e.g., confirmed, probable, suspect)
- Describe and orient the data in terms of
time, place, and subject
Orient the Data in Terms of TIME
• Epidemic “epi” curve: Graphic plotting of distribution of cases (y axis) by time of onset (x axis), using an appropriate time interval
• Can assess:
– Magnitude of the outbreak
– Possible mode of spread
– Duration of the epidemic
• A time interval of 1⁄4 to 1⁄2 an incubation period works best
Types of epidemic curves
Point Source Epidemic
Continuous Common Source
Propagated Epidemic
Steps in Creating an Epidemic Curve
- Identify date of onset for first case
- Set the time interval
- Create X-axis lead and end periods
- Assign area equal to one case to Y-axis • Plot cases
- Mark critical events in the outbreak
- Add labels
Orient the Data in Terms of PLACE
• Mapping can provide clues regarding – Source of agent
– Nature of exposure
• Dissemination of pathogens and who is at risk may be affected by
– Water supply
– Milk distribution routes
– Sewage disposal outflows – Prevailing wind currents
– Et cetera
Orient the Data in Terms of SUBJECT
• Knowing
– Number of cases
– When they became ill – Where they became ill – General characteristics
will help in generating hypotheses and targeting prevention
- Develop hypotheses
Hypothesis Generation
• Probably have good sense of source by this point in investigation
• Hypothesis generating questionnaires
– For foodborne outbreaks will ask about food consumption patterns in general
• Consider “new” sources of infection but don’t forget the “usual” sources
