Outbreak Investigations Flashcards
Why conduct an outbreak investigation?
- determine etiology (i.e. cause of source) quickly to initiate control measures
- provide timely response to public concerns
- investigations of outbreaks is a core function of health departments at various levels and substantial resources are used for these activities
What are the steps of outbreak investigations?
Information Gathering Phase
1) determine existence of epidemic
2) develop a case definition
3) identify cases and population at risk
4) obtain information - person, place, and time
5) collect specimens for lab analysis
Inferences Phase
6) Analyze data
7) develop, test, and refine hypotheses
8) implement control measures
9) prepare report and disseminate findings
How do you determine the existence of an epidemic?
Info from local health officials, surveillance data (observed vs. expected). Also can gather from medical practitioners, hospital records, registries, labs, affected persons/groups, media.
But, beware of changes! Changes in local reporting practices; improvements in diagnostic procedures; increased local/national awareness; sudden population changes. (may need to acquire additional data)
How do you develop a case definition
person: type of illness/clinical criteria (“person with…”)
place: location of suspected exposure
time: when did symptoms/exposure occur?
Clinical features and known causes. What tests to confirm diagnosis? Start with a simple case definition and refine as you go.
How do you identify cases and population at risk?
Identify sources for finding cases. Collect info likely to provide clues to determine population at risk. (natural history of the illness, characteristics of the ill)
Sources of cases from healthcare practitioners, PH laboratories, the public, contact tracing, cruise ship/hospital/nursing home
How do you obtain information?
characteristics of persons affected: demographics, potential exposures, place, time of occurrence
How do you collect specimens for lab analysis?
serologic tests, blood, stool. X-rays, food/environmental samples
How do you analyze data in outbreak investigations?
Calculate attack rates - defined as the cumulative incidence of illness during an epidemic in a group of people who are “at risk”
attack rate = (number of people at risk in whom a certain illness develops) / (total number of people at risk)
total number of people at risk will include cases and non-cases, can be designated for a given exposure
Practice Problem
How do you attack rate?
number of people at risk in whom: (a certain illness develops)/(total number of people at risk)
What is a primary case?
a person who acquires the disease from the exposure
What is a secondary case?
a person who acquires the disease from exposure to a primary case
