outbreak investigation Flashcards
what is the difference and similarities between outbreak and epidemic
similarities:
more cases of disease than expected
differences:
outbreak is a localized increase in disease cases (an outbreak of Legionnaires’ disease in a hotel with contaminated water system)
epidemic is a widespread and rapidly spreading, affecting a much larger population across multiple areas (covid, ebola)
define disaster cluster
unusual grouping of disease cases in one place and time w/o implying the no. of cases is higher than expected
(hurricane cluster - multiple hurricanes or wildfire cluster - multiple wildfires)
it can be the first indication of a larger outbreak or epidemic but they can also occur by chance or due to other factors that may not be immediately apparent.
disease clusters
briefly explain on how does outbreak gain attention of the public health agencies
epidemiologic surveillance systems:
continuous monitoring and analysis of data related to the occurrence and spread of disease = public health officials investigate further
direct notification:
from healthcare providers, laboratories or school (school reporting high absenteeism due to illness or laboratories reporting +ve results for a notifiable disease)
factors affecting the decision to mount an outbreak investigation
[PPAASI]
Ability to confirm that the observed cases is significantly greater than expected
Scale and severity of the outbreak (how widespread the cases r)
If the outbreak disproportionately affects an identifiable sub-group (ex: elderly, children)
Potential for spread
Political and public relations considerations (attract media attention)
Availability of resources (have sufficient staff, fund and lab capacity to conduct)
main objective of outbreak investigation
help guide disease prevention and control strategies
briefly explain the relative priority of investigative and control effects during an outbreak, based on knowledge of the source, mode of transmission and causative agent
known source/ MOT + known causative agent =
known source/ MOT + unknown causative agent =
unknown source/ MOT + known causative agent =
unknown source/ MOT + unknown causative agent =
known source/ MOT + known causative agent =
highest priority: control
lowest priority: investigation
known source/ MOT + unknown causative agent =
highest priority: investigation & control
unknown source/ MOT + known causative agent =
highest priority: investigation
lowest priority: control
unknown source/ MOT + unknown causative agent =
highest priority: investigation
lowest priority: control
what are the objectives of outbreak investigation
[PAARII]
Asses range and extent of the outbreak
Reduce the no. of cases associated w the outbreak
Identify new disease syndromes
Identify new causes of known disease symptoms
Assess the effectiveness of currently employed prevention strategies
Provide for good public relations and educate the public
briefly explain the agencies responsible for outbreak investigation
local health departments
CESU: City Epidemiology and Surveillance Unit
MESU: Municipal Epidemiology and Surveillance Unit
higher level health agencies
RESU: Regional Epidemiology and Surveillance Unit
DOH-EB: Department of Health - Epidemiology Bureau
what are the 10 steps in outbreak investigation
- prepare for fieldwork
- establish the existence of an outbreak
- verify the diagnosis of cases
- construct a working case definition and search for additional cases
- conduct a descriptive epidemiological study
- develop hypotheses in
- evaluate hypotheses
- reconsider hypotheses, conduct additional studies if necessary
- implement control and prevention measures
- communicate findings
step 1 in outbreak investigation: prepare for fieldwork
scientific aspect
working knowledge/ backgrnd on public health concern
administrative aspect
- travel arrangements
- supplies and equipment
-administrative and scientific contacts
personal aspect
- clear understanding of the role in the field
- familiarity of the chain of authority involved in the process
step 2 in outbreak investigation: establish the existence of an outbreak
to confirm that there is actually an outbreak, certain criteria need to be met.
- use standard diagnostic criteria
- compare observed rate to expected rate
step 3 in outbreak investigation: verify the diagnosis cases
- ensure disease in question have been correctly identified and diagnosed
- rule out lab error - check the increase in reported areas are not due to mistake or errors in lab testing
how to verify cases in an outbreak investigation
review clinical findings and lab results
check if said result r consistent with what is known clinically and epidemiologically of the disease
how to determine the expected baseline rate in the establishment of existence in an outbreak
to know the “normal”
- national surveys
- special registries
- data from neighboring localities
- publishing literature
how to make comparison in the establishment of existence in an outbreak
look at the no. of cases in
- previous week/ months
- same period from previous years
step 4 in outbreak investigation:
construct a working case definition and search for additional cases
case definition
- a set of standardized criteria used to determine whether someone should be classified as having the disease of interest
- restricted by time, place and person
systematic case finding
- search for previously unidentified/ unreported cases that fit the criteria
in simple terms:
consistent identification of true cases. to capture all possible cases meeting that definition rather than relying on initially reported cases
how do we stratify cases in construct a working case definition in an outbreak
confirmed cases (positive lab test)
probable cases (symptoms but no test done)
possible cases (some symptoms but doesn’t meet full criteria)
step 5 in outbreak investigation: conduct a descriptive epidemiological study
determine the range and extent of the outbreak (determine hoe widespread is - the geographic area, no. of ppl time period)
assess possible source of exposure (ex: contaminated food/water), mode of transmission (airborne, contact), incubation period, environmental host or agent factor
generate hypotheses abt outbreak (abt what factors led to and drive this outbreak)
in simple terms:
aims to characterize and describe the key details of an outbreak
step 6 in outbreak investigation: develop hypothesis
address:
- source of exposure to etiologic agent
- MOT
- next step in investigation
- future control measures
search for specific exposures that have the strongest association with the disease (to test the hypotheses). this is done by calculating measures
- relative risk RR (how much more likely exposed ppl r to get disease)
- odds ratio OR (odds of exposure in case vs. non cases)
- risk difference RD (diff in disease risk btwn exposed and unexposed)
investigate notable expectations (examine cases that dont fit the main hypotheses)
step 7 & 8 in outbreak investigation:
7 - evaluate hypotheses
8 - reconsider hypotheses, conduct additional studies if necessary
hypotheses r re-examined, refined and tested throughout the investigation
tested using
- qualitative methods (gather descriptive info through interviews and observations)
- quantitative epidemiological (analyze data statistically to measure association btwn exposure and disease)
- investigation and laboratory/ environmental studies (test samples, food, water etc to identify contaminant)
what are the specific analytical studies may be conducted in steps 7 and 8
retrospective cohort study
- small, well circumcised outbreak
- incidence is high
case-control study
- large, poorly-circumcised outbreaks
- incidence is low
step 9 in outbreak investigation: implement control and prevention measures
levels of prevention
- primordial prevention
- pri prevention
- sec prevention
- tertiary prevention
natural history of disease
- stage of susceptibility
- stage of subclinical disease
- stage of clinical disease
- stage of recovery, disability or death
the epidemiological triad
- agent
- host
- environment
step 10 in outbreak investigation: communicate findings
it is not complete until the results r disseminated to the public and the profession
- initial informants
- persons involved in the investigation
- public health agencies
- community
forms
- oral briefing
- written report
it is the visual study of the magnitude and time trend of outbreak
the epidemic curve
the epidemic curve
x-axis:
y-axis:
x-axis: no. of cases (%)
y-axis: timeline
what information r obtained from the epidemic curve
Probable period of exposures
Nature of the epidemic
Future courses of the epidemic
Effectiveness and timeliness of prevention and control measures
describe the outbreak in terms of place
dot maps:
Document geographic extent of probs and can provide evidence of clustering
maps of area-specific rates:
Compare areas w population of unequal sizes
describe the outbreak in terms of person
Identify high risk grp
Frequency of disease shld be described by age and sex (at minimum)
Person factors relevant to outbreak investigation
- Demographic characteristics
- Personal activities and practices
- Genetic predisposition
- Physiological states
- Concurrent disease and immune status
briefly explain the patterns of epidemic curve
point source epidemic:
curve has upslope but a more gradual downslope
Person exposed to the same source over a relative short period
continuous common source epidemic:
curve has plateau instead of a peak
Exposed duration is prolonged
intermittent common source epidemic:
curve is irregularly jagged
Exposure to the agent is sporadic over time
propagated epidemic:
curve has a series of progressively taller peaks one IP apart
Disease agents spread from one person to another w increasing. of cases in each generation
