DISEASE E&E (Measuring Disease 3)

Question 1

Two components of animal health/disease surveillance:

Answer 1

1. Early detection
2. Early response

Question 2

Animal health surveillance:

Answer 2

-identifies important disease events in animal populations
-allows farmers, vets and government control agencies to develop timely and appropriate responses to eradicate, control or mitigate adverse effects

Question 3

Surveillance defined by WHO:

Answer 3

ongoing systematic collection, collation, analysis, and interpretation of data and the sharing of that info to those who need to know so action can be taken

Question 4

Early detection:

Answer 4

disease monitoring system
-a defined level or threshold of disease at which an intervention should take place

Question 5

Early response:

Answer 5

-defined set of interventions that will be taken if and when the threshold is reached
-interventions will vary depending on disease and its public health or economic significance

Question 6

4 general purposes of disease surveillance:

Answer 6

1. Demonstrating freedom from disease
2. Early detection of disease
3. Measuring the level of disease
4. Finding cases of disease

Question 7

For disease that are not currently present: (purposes)

Answer 7

-early detection
-demonstrate freedom

Question 8

Diseases that are present: (purposes)

Answer 8

-case finding
-measure level of disease

Question 9

Diseases that are NOT currently present or normally present:

Answer 9

-exotic diseases
-emerging diseases
-new diseases
-epidemic diseases
- poopy pants

Question 10

Why demonstrate freedom?

Answer 10

1. Trade access
2. Trade barriers
3. Stopping control or eradication measures that have been in place
4. Public health measures could be lifted
5. Political reasons

Question 11

Why early detection?

Answer 11

-early response
-prevention of spread to other countries

Question 12

Diseases that are present:

Answer 12

-recognized endemic diseases
-measure other facts that might limit market access (antimicrobial usage, resistance, animal welfare practices)
*define what is normal at the population level

Question 13

Doing single measures at one point in time:

Answer 13

*prevalence
-prioritization of disease/risk analysis
>which disease have greatest economic impact

Question 14

Doing multiple measures of disease for comparison:

Answer 14

-spatial distribution of disease
-temporal distribution

Question 15

Spatial distribution of disease:

Answer 15

-understanding spatial risk factors
-establishing disease free zones
Ex. maybe could have a control point in Manitoba if FMD broke out in eastern Canada

Question 16

Temporal distribution:

Answer 16

-monitoring control programs
-early detection of changes in endemic disease (trends)
-identify risk factors for disease and production practices that influence disease status

Question 17

Finding cases of disease:

Answer 17

-identifying individual cases or individual outbreaks
-usually part of a disease control program

Question 18

Concepts and principles to meet surveillance objections:

Answer 18

1. Timeliness
2. Population coverage
3. Representativeness of surveillance sample

Question 19

Representativeness of surveillance sample:

Answer 19

-representation (prevalence in sample=prevalence in population
-risk based (prevalence of sample > prevalence in population)
-biased (prevalence in sample (not equal) prevalence in population

Question 20

Early detection surveillance system should:

Answer 20

-be continuous
-have comprehensive coverage of the population
-be sensitive with a very low design of prevalence

Question 21

Demonstration of freedom surveillance system:

Answer 21

-does NOT need to be continuous, but may be intermittent
-can use risk-based sampling to increase efficiency
-uses a higher design prevalence than early detection

Question 22

Measuring disease surveillance system:

Answer 22

-can be periodic
-should be based on representative sampling to avoid bias
-needs a large enough sample to give adequate precision

Question 23

Case finding surveillance system:

Answer 23

-use comprehensive coverage of population
>risk based approaches can focus on high risk parts of the population
-be ongoing
-have good individual herd or animal sensitivity

Question 24

Surveillance systems are characterized by:

Answer 24

-timing of data collection
-source of data
-sampling method
-level of detail/case definition

Question 25

Types of surveillance systems:

Answer 25

1. Passive surveillance
2. Active surveillance

Question 26

Passive surveillance

Answer 26

-using existing data that is available
-“observer initiated” data collection
-less expensive
-requires significant effort to collect and analyze data
-used to identify new and emerging diseases
*continuous but NOT representative data

Question 27

Steps in a diagnosis being made:

Answer 27

1. Disease animal shows clinical signs of disease
2. Producer recognizes animal is sick
3. Producer consults vet
4. Vet examines animal and takes samples
5. Samples submitted to diagnostic lab
6. Appropriate tests conducted to detect disease
7. Diagnosis made

Question 28

Disadvantages of passive surveillance systems:

Answer 28

-samples are NOT representative of entire population
-info about population is lacking
-can’t always extrapolate to the general population
-certain diseases are suited for it (stigmatised, mild, ones with unfavorable cost-benefit ratios)

Question 29

Active surveillance:

Answer 29

-purposeful collection of info often targeting a specific disease
-“investigator-initiated” data collection
-more expensive
-more accurate estimate of disease frequency
Ex. surveys, mass screening programs

Question 30

Larry Brilliant and Smallpox surveillance:

Answer 30

*great example of active surveillance
-early detection…early response!

Question 31

Risk based or targeted surveillance:

Answer 31

-target at animals or populations that are more likely to have the disease or in an area that it is more likely to be introduced
-usually used for freedom from diseases or early detection
-helps to optimize use of surveillance resources
Ex. surveillance for BSE in Canada

Question 32

Surveillance for BSE in Canada:

Answer 32

-disease is very rare
-random sampling would be very INEFFICIENT way of finding cases
-4D: diseased, down, dying or dead
-*OSE has a point classification system for risk-based surveillance

Question 33

Sentinel surveillance:

Answer 33

a “hazard-specific” surveillance system
-smaller numbers of animals of know immune status
-“canary in a coal mine” type of surveillance
-sentinel units are chosen to intensively monitor over a period of time

Question 34

Observe sentinel units over a period of time:

Answer 34

-repeated visits to sentinel sites or sentinel animals
-antibody status often used to determine exposure
-measuring freedom from disease
-early warning system
-geographic distribution

Question 35

Abattoir surveillance:

Answer 35

-inexpensive as animals are already being inspected and processed
-can cover a large number of animals
-relatively constant supply of data
-can be both active and targeted
-skilled observers are present
-potential problem with biased sample

Question 36

Syndromic surveillance:

Answer 36

-group clinical diseases into syndromes rather than specific diagnoses
-indicator-based surveillance
-utilize clinical reports
-large amounts of data required
-simple, cheap and easy to obtain
-useful for early detection
*need to follow up suspicious events
-false alarms will occur
Ex. diarrhea

Question 37

Random sampling:

Answer 37

-every member of the population should have an equal probability of being sampled in the surveillance system
*method used will be dependant on goals of the surveillance system

Question 38

Sampling considerations?

Answer 38

-what is the primary objective of the surveillance system?
-do we need a representative sample or a risk-based sample?
-what is the sampling unit?
-how accessible is the population?

Question 39

Simple random sampling:

Answer 39

-select a fixed percentage using a formal random process
-requires a SAMPLING FRAME (ex. list)
-will provide an unbiased estimate of prevalence
-larger sample sizes provide more precise estimates
-every individual has an equal opportunity of being sampled

Question 40

Systemic random sampling:

Answer 40

-sampling units are selected from a sampling frame at regular intervals
-Ex. every fifth farm or every third animal
-calculate the required sample size
*divide expected population by the sample size required to get the appropriate interval
-can introduce bias if animals don’t enter facility randomly

Question 41

Stratified random sample:

Answer 41

• source population divided into strata based on factors know to affect the outcome (ex. breed, gender, herd size)
  >systematic sampling is used for selecting the sample units
  -more flexible than simple random
  -can have equal numbers or sample proportional to the size of the strata

Question 42

Cluster sampling:

Answer 42

-each sample units is an aggregate of study units (ex. herds, litters)
-individual animal is still unit of interest
-randomly sample herds via simple, systematic or stratified random methods
*then sample all individual units within each unit
-infectious disease clusters within herds

Question 43

Advantage of cluster sampling:

Answer 43

-less cost to sample more individuals

Question 44

Disadvantages of cluster sampling:

Answer 44

-may lead to an underestimate of the variability of the disease in the broader populations of individuals

Question 45

Multistage sampling:

Answer 45

-random sampling methods at 2 levels
-randomly sample herds (primary sampling units)
-randomly sample individuals within the herds (secondary sampling unit)

Question 46

If more variation between herds: multistage sampling

Answer 46

• may want to sample more herds and less individuals

Question 47

Sample size calculations:

Answer 47

-number of formulas that can be used
-if rare disease=have to sample more animals to try and find it
-if want an accurate estimate=must sample more animals

Question 48

Challenge in building good surveillance systems:

Answer 48

-buy in and participation
-data integration and analysis
-confidentiality and data sharing
-maintaining vigilance
-diagnostic tests for identifying disease

Question 49

Who is on the front line of disease surveillance?

Answer 49

-practicing vets and knowledgeable producers

Question 50

Classical surveillance activities:

Answer 50

1. Mandatory reporting (federally and provincially reportable diseases)
2. Active surveillance for specific diseases
3. Passive surveillance at labs, abattoirs, markets and dead stock
4. Export testing and certification

Question 51

Canadian animal health surveillance network (CAHSN):

Answer 51

-tried to standardize and merge data from different places
-an independent, member-drive “network of networks” for effective, responsive, and integrated animal health surveillance in Canada

Question 52

Provincial or regional activities:

Answer 52

-Alberta Vet Surveillance Network
-western Canadian animal health network (WeCAHN

Question 53

Sector or animal type activities:

Answer 53

-Canadian cow-calf surveillance network

Question 54

Zoonotic disease and public health:

Answer 54

-rabies surveillance and control programs
-tick surveillance for lyme disease