Investigating an Outbreak Flashcards
what is an outbreak?
outbreak/epidemic exists when there are more cases of a particular disease than expected in a given area or among a specific group of people over a particular period of time
why do we investigate an outbreak? (6)
- to control and prevent disease
- to determine the severity and risk to others
- for research opportunities and to gain additional knowledge
- training opportunities
- program considerations (training and prevention)
- public, political, or legal concerns
what are the 7 steps of investigating an outbreak?
- prepare for field work
- verify outbreak
- plot epidemic curve
- calculate attack rates
- determine source of epidemic
- recommend control measures
- follow up
what are the 5 things that happen in step 1 of investigating an outbreak (preparing for field work)?
- research what is known about the disease or symptoms
- learn about demographics and customs of local population
- make admin and travel arrangements
- build your team with clear delineation of responsibilities and assignments
what are the 4 things that happen in step 2 of investigating an outbreak (verifying outbreak)?
- establish a case definition that is non-ambiguous with clinical/diagnostic verification if possible with person/place/time descriptions
- identify and count cases of illness
- determine if disease is above endemic levels or if looking at a different disease with similar symptom
- develop and administer a questionnaire to determine demographics, behaviors, and exposures
how is an epidemic curve plotted?
number of cases on the y axis by their date or time of onset (x axis)
what does the overall pattern of an epidemic curve tell you?
the increase, peak, and decrease can tell type of epidemic and incubation period
what can outliers of an epidemic curve tell you?
if a case is unrelated, early or late exposures, index case, secondary cases
describe the epidemic curve of a vector borne disease (3)
- starts slowly (climate effects can modify)
- the time between the 1st case and peak is comprable to incubation period
- slow tail, will rise again or repeat until run out of susceptible people
describe the epidemic curve of a point source epidemic
large population exposed over a short period of time so high peak at beginning and then tapers off; most common form of transmission for food-borne disease
describe the epidemic curve of a continuing common source or intermittent exposure epidemic
several peaks, cannot isolate incubation period
give an example of a point source epidemic
legionnaire’s disease
give an example of continuing common source or intermittent exposure epidemic
cholera
describe the 3 steps in step 4 of investigating an outbreak (calculate attack rates)
- calculate attack rate for each possible risk factor
- if there is an obvious commonality for the outbreak, calculate attack rates based on exposure status (a community picnic, then later you can calculate this to individual items at the picnic)
- if there is no obvious commonality for the outbreak, calculate attack rates based on specific demographic variables
describe step 5 of investigating an outbreak (determining source of epidemic)
attack rates can point statistically to the factor most closely associated with becoming a case, but it may require more than one risk factor to become a case, so ask if there are case that are NOT associated with your source (like malaria not from a mosquito)