Outbreak investigation Flashcards
occurrence of more cases of disease than expected in a given area or among a specific group of people over a
particular period of time
Outbreak
occurrence of more cases of disease than expected over a larger area than that experienced in an outbreak
Epidemic
aggregation of cases in a given are over a period without regard to whether the number of cases is more than expected
Disease Cluster
usually, the size of the population at risk is unknown
harder to prevent and control
Disease Cluster
First COVID-19 Infections in the Philippines
December 2019
January 2020, DOH informed the countr
main objectives of Outbreak Investigation
to help guide disease prevention and control strategies
Agents responsible for Outbreak Investigation
Local : mesu, cesu
Higher: resu, doh-eb
what are the steps of outbreak investigation
- Prepare for field work
- Establish the existence of the disease
- Verify the diagnosis of a case
- Construct a working case of definition and search for additional cases
- Conduct a descriptive epidemiologic study
- Develop hypotheses
- Evaluate hypotheses
- Refine/ reconsider hypotheses, conduct additional studies if necessary
- Implement control and prevention measures
- Communicate findings
who made the Steps in Outbreak Investigation
US CDC prescribed investigatory steps(1992)
when will the prepare for field work begin
begins when the decision from higher health agencies has been made
assembling a multidisciplinary outbreak investigation team and gathering the necessary equipment and supplies to collect the clinical environmental sample
Prepare for field work
- working knowledge or background on the public health concern
- e.g. different literature articles and studies
Scientific Aspect
- travel arrangements
- supplies and equipment
- administrative and scientific
contacts - communication line from the internal and external stakeholders
- e.g. extra equipment especially disposable equipments
Administrative Aspect
- clear understanding of the role in the field
- familiarity of the chain of authority involved in the process
- expertise in clinical medicine, epidemiology, environmental health, microbiology, and et
Personal Aspect
review the existing surveillance baseline data
Establish the existence of an outbreak
allows the confirmation that reported cases actually have the disease being reported
standard diagnostic criteria
How is comparison carried out?
▪ compare the currently observed number of cases in previous weeks or months
▪ compare the currently observed number of cases with the number of cases in a comparable period from previous years
▪ needs certain individuals such as Medical Technologists and Doctors
▪ to ensure that disease in question has been
properly identified
Verify the diagnosis of cases
the multidisciplinary clinical team should create a case definition and begin to identify cases that may be associated with the outbreak
Construct a working case of definition and search for additional cases
▪ to rule out laboratory error as the cause of the reported increase in the number of cases
Verify the diagnosis of cases
in constructing a case definition, we should consider what?
consider the time period, incubation period, and location
standard set of criteria for deciding whether an individual should be classifies as having the health condition of interest
Case Definition
Case Definition includes
- clinical criteria – signs and symptoms
- restrictions by time, place, and person – descriptive epidemiology
How do we stratify case?
▪ Confirmed
o underwent RT-PCR or there is a
laboratory confirmation
▪ Probable
o meets clinical criteria
o contact of a probable or confirmed
case
▪ Possible (Suspected)
o signs and symptoms only, no
confirmation yet
▪ summarizing the person, place, and time variables
▪ uses different bars, charts and epidemic curve
Conduct a descriptive epidemiologic study
give one objective of Conduct a descriptive epidemiologic study
to determine range and extent of the outbreak
to assess the possible source of exposure, mode of transmission, incubation period, environmental, host, or agent factors
to generate hypotheses about the outbreak
▪ a visual display of the magnitude and time trend of the outbreak
▪ a histogram or a bar chart that shows the distribution of cases over time
Epidemic Curve
essential tool in an outbreak investigation and a key feature of descriptive epidemiology
Epidemic Curve
represents the number of cases (%)
y axis
represents a timeline (should
begin before the epidemic period, and extend to the period after the epidemic is over)
x-axis
persons are exposed to the same
source over a relative short period o the curve
has a steep upslope but a
more gradual downslope
only peaks one time
Point Source Epidemic (Common Point Source Outbreak)
disease agent spread from person to
person with increasing number of
cases in each generation
Propagated Epidemic
lasts longer than the common source
epidemic
Propagated Epidemic
o exposure to the agent is sporadic over time
o the curve is irregularly jagged
Intermittent Common Source Epidemic
exposure duration is prolonged
the curve has a plateau instead of a
peak
exposure persists
Continuous Common Source Epidemic
serve to document geographic extent
of the problem, and can provide
evidence of clustering
Dot Maps
suitable when comparing areas with
populations of unequal sizes
Maps of Area-specific rates
frequency of disease should be
described by ________ (at minimum)
age and sex
in an outbreak investigation, hypotheses should address:
- source of the exposure to the etiologic agent
- modes of transmission
- next steps in the investigation
- future control measures
how is search for specific exposures that have
the strongest association with the disease
one by computing for the Relative Risk/OR/Risk Difference
describe Retrospective Cohort Study
o determining present to future
o small, well-circumcised outbreaks
o incidence is high due to the exposure time and true disease
hypotheses are re-examined, refined, and tested throughout the investigation
Evaluate hypotheses
describe Case-Control Study
o determining from past to present
o large, poorly-circumcised outbreaks
o incidence is low due to information or knowledge of the infected individual through surveys and questionnaires
how to Implement control and prevention measures
epidemiological triad
levels of susceptibility
levels of prevention
give to the necessary agencies such as local health agencies, local municipalities, or higher registries (DOH)
Communicate findings
investigation is not complete until the results are _____
disseminated to the public and the profession
Forms of the outbreak investigation
o oral briefing
o written report
o media
