Week 8 Flashcards
outbreak
An outbreak or epidemic exists when there are more cases than expected of a particular disease among a specific group of people and/or in a given area, over a particular period of time
pandemic
world wide epidemic
epidemic
more cases than usual
outbreak
same as an epidemic; may be smaller number of cases, area or population
cluster
group/aggregation of cases usually in one specific location
endemic
permanent/regular disease incidence
why do outbreaks occur?
New appearance of an infectious agent (Or toxic material) from the environment or from an infected source
Arrival of susceptible people to an environment with an endemic pathogen
Introduction of effective route of transmission from source to susceptible population (e.g. climate change bringing new mosquito species)
oubtreak investigation had
primary goals
secondary goals
factors that impact our process and decision making
Outbreak investigation- primary goals
Identify pathogen or source
Control
Prevent future outbreaks
All the above in a timely manner
Outbreak investigation- secondary goals
Learn more about a disease
Training opportunity
Outbreak investigation- factors that impact our process and decision making
Case numbers
Disease severity
Risk to others
public/political/legal concerns
Steps of an outbreak investigation
Prepare for field work
Verify the existence of the outbreak
Confirm the diagnosis
Define and identify cases
Describe/orient data (person, place, time)
Develop hypotheses
Evaluate hypotheses
Refine hypothesis/perform additional studies
Implement control and prevention measures
Communicate findings
Step 1: prepare for field work
Epidemiological knowledge and homework What are the usual risk factors? Previous outbreaks? Supplies and equipment Competent laboratory Portable computer, phone, supplies Team composition Who should be in team? Who is in charge? Statistical advisors, public relations, local information Administrative Transport and communication travel, cash, credit cards immunisation, prophylaxis Personal
Step 2: verify existence of outbreak
Defined as ‘more cases than usual’ What is ‘usual’? Must have access to baseline data Specific to region Specific to current time Where are the cases? Surveillance: monitoring of disease in populations passive, active, sentinel (targeted) surveillance Sources of information: Surveillance records local/state health departments Other registries (Hospital discharge records, death records, cancer or birth defect registries) Clinicians Labs Schools
Some causes of false alarms
Change in surveillance/policy of reporting
Change in case deifinition
Improved diagnosis (new test, increased GP awareness, new doctor in town)
False positives from errors in diagnostic tests
Increased public awareness (media coverage leading to demand for tests)
Increased reporting (performance incentives)
Step 3: confirm diagnosis
Review clinical findings Review lab results of cases Be as specific as possible about the causative agent ‘outbreak strain’ of bacteria/virus May need specialised lab input Talk to cases
Step 4: define and identify cases
Case definition is important and can change
Sensitive vs specific
Components include:
Clinical features (bloody diarrhoea)
Person- who to include and exclude
Place- place of residence, where they ate
Time period of interest
Lab results
Divide into:
Confirmed- usually lab confirmed
Probable- lab results not available
Possible- often less stringent clinical criteria
Case finding
Use as many sources as you can
Health care facilities and labs
Alert the public and ask cases to identify themselves
Identify people in place of interest at time of potential exposure and directly contact them
Barriers to case detection
Lack of public understanding Lack of communication with the public On existence of outbreak On role of imported health care workers Community distrust Lack of inclusive planning for outbreak resolution
Step 5: describe and orient the data
Time: draw an epidemic curve
Number of cases on y axis
Time on x axis
May provide hints about source of outbreak
Place: map the data
Person: explore data according to personal characteristics
Steps 6-8: develop/test/refine hypothesis
What is the source of the infection?
Case control or cohort study?
Other investigations?
step 9: control and prevention
Once source of outbreak has been identified, aim to break links in chain of infection Do as soon as possible Examples: Remove contaminated food Sterilise contaminated water Spray mosquitoes/destroy breeding sites isolation/treatment of cases Immunise contacts/susceptibles Prophylactic medication Behaviour modification
step 10: communicate findings
Must occur throughout outbreak investigation
Investigation team/partners/press/public
Prepare timely reports
Initial oral briefing (at time leaving the field)
Final written report
Publications
Clearly state facts
Beware of legal implications
Aim to improve practice
Down stream factors
helping done in the moment
road design, safety enforcement, excessive speed, driver fatigue, alcohol consumption, use of illicit drugs, use of a mobile phone, absence of effective trauma care
upstream factors
what is done to prevent happening again
car use as influenced by fossil fuel energy policies, taxation on alcohol, policing traffic laws, resource allocation to hospital trauma units
linear regression
outcome variable must be continuous
exposure may be numerical or categorical
strong negative
-0.8 - -1
moderate negative
-0.5 - -0.8
weak negative
0 - -0.5
weak positive
0 - 0.5
moderate positive
0.5 - 0.8
strong positive
0.8 - 1
linear regression assumptions
Outcome variable follows normal distribution (evaluated using histogram or box plot)
Relationship between outcome and covariate is linear
Constant variance of outcome across different values of the covariate remains the same across different values of the covariate
residual/prediction error
difference between observed and predicted values
coefficient of determination
r^2
