07. Outbreak Epidemiology Flashcards
Definition
The investigation of a disease cluster or epidemic with the goal of controlling and preventing further disease in a population
How do you know an outbreak is occurring?
Typically first identified at the local level
- Report from doctor’s office, hospital, nursing home or laboratory
- Analysis of routine public health surveillance reports
- Analysis of “syndromic surveillance” reports
Why Investigate outbreak?
Primary motivation: prevent the spread of disease within initial population & prevent spread to additional populations
Prevent future similar outbreaks
Provide scientific explanation for the event
React to and calm the public
Outbreak Investigation Steps (9)
Prepare and plan for the investigation
Confirm the existence of an outbreak
Identify and count cases
Collect risk information
Analyze data in terms of time, place, and person
Collect specimens for laboratory analysis
Institute control measures
Formulate and test hypotheses (Choose a study design)
- Communicate the findings
Prepare and Plan for Investigation
- Identify your team members
- Epidemiologists, healthcare professionals, laboratorians, sanitarians
- Small outbreaks – “team” might be one or two individual
- Large, multijurisdictional outbreaks - may involve local & state public health / federal entities
- Assign responsibilities to team members; who will lead?
- Research potential causes
Confirm the Existence of Outbreak
- Are there more cases than you would expect for that disease and setting?
- Healthcare providers, local public health, local surveillance data is useful
- Need to take into account the population affected. E.g. nursing home vs healthy adult population
- In some cases in the US, when a disease is rare and serious, a single case of disease is considered an outbreak. E.g. human rabies
- Has some change occurred that would make it look like an outbreak is occurring?
Identify and count cases
Develop a case definition. criteria:
- Population of concern (Person)
- Location(s) of interest (Place)
- Time period of interest (Time)
- Clinical features
Early Case Definition: emphasis on sensitivity
Later Case Definition: emphasis on specificity
Cases may be separated into CONFIRMED and PROBABLE
Confirmed: Typically there is laboratory confirmation for a pathogen. • In some instances, confirmed cases are those with an illness compatible with the case definition who have an epidemiologic link with a laboratory confirmed case. E.g. pertussis
Probable: Symptoms are compatible with case definition, but there is not laboratory confirmation of a pathogen
Line Listings
Each row represents a person
Each column represents a different variable
Line listings should include:
- Identifying Information (name, address, phone number)
- Demographics (age, sex, race)
- Clinical information (symptoms, date of onset, laboratory results)
- Risk factor information (epi link to another case, food and other known exposures)
Identify Population at Risk & Additional Cases
Identify the population at risk or the exposed group in which you will seek to identify additional cases
- Will depend on the setting
- Not always possible to identify the entire population at risk
Target additional case finding within the designated population
- Utilize available surveillance data
- Reach out to hospitals, emergency rooms, medical providers
- question known cases about others who might have been exposed
Collect Risk Information
Tabulate in Terms of Person / Place / Time (Descriptive Epi):
Person: Line Listing – method to quickly summarize pertinent variables E.g. number of cases, age range, number of cases hospitalized
Place: Spot Map – Plot the area where affected people live, work, or may have been exposed
Time: Epidemic Curve – Depicts frequency of cases over time by plotting number of cases by date or time of onset.
- Point source epidemic: population exposed at one point in time
- Common source epidemic: population continuously exposed
- Propagated outbreak: involves person to person spread through population
Perform Laboratory Analysis
Collect and test appropriate specimens
Hypotheses regarding the suspected agent and source should guide the lab testing
Specimen examples: Food, environmental (e.g., water), clinical (e.g., stool, blood, respiratory, wound)
Lab confirmation may be difficult or complicated
Implement Control Measures
Initiate ASAP!
Recalling/destroying contaminated food • Sterilizing contaminated water • Remove infectious food handler from job • Destroying mosquito breeding sites • Closing affected facilities • Isolating affected individuals, including in medical care facilities • Recommending therapeutic agent or prophylactic agent (e.g. vaccine) • Educate public regarding risk and prevention • Development of procedural changes, guideline, regulations or laws that will prevent similar outbreaks
Formulate and Test Hypotheses
Broad hypothesis: Individuals who ate from the buffet at Restaurant X are at increased risk of developing gastrointestinal illness over those who did not eat at the buffet.
Specific hypothesis: Individuals who ate tuna fish salad from the buffet at Restaurant X on a specified date are at increased risk of developing norovirus over those that did not eat the tuna fish.
Next step: Choose appropriate study design to test your hypothesis
Cohort Studies
Study of a group of people forward in time (prospective) and determine if they get sick
Some exposed / Some not exposed to risk factor (e.g. food item) • Best design when the exposed population can be easily identified and counted
Outbreaks where the exposure has occurred at a specific event (party) or at a specific place (school, cruise ship) are well suited for cohort studies
Relative risk
