Surveillance/Monitoring Systems

Question 1

What is the difference between monitoring and surveillance?

Answer 1

MONITORING = continuous, adaptable process of collecting data about diseases and their determinants in a given population - collecting information

SURVEILLANCE = specific case of monitoring in which control/eradication measures are implemented - act on a finding

Question 2

What are the 2 goals of MOSS (monitoring and surveillance systems)?

Answer 2

1. early warning of change and health status of any animal population
2. provides evidence about the absence of diseases or determines the extent of disease that is known to be present (commonly for trade)

Question 3

Why is surveillance done?

Answer 3

provides information that is critical for decision-making in disease control and prevention

• How much disease is there?
• What impact is this disease having on animals, public health, farmers, and trade?
• Is prevalence increasing, decreasing, or staying the same?
• Where does disease occur and what are the spatial patterns and trends?

Question 4

In what 2 ways can surveillance be classified?

Answer 4

1. according to collection of data: active vs. passive
2. according to disease focus: targeted vs. general (no diagnoses in mind)

Question 5

What are 3 additional ways to classify surveillance?

Answer 5

1. syndromic - clinical signs
2. risk-based - risk factors
3. participatory - general public

Question 6

What is active surveillance? How is the population determined?

Answer 6

systematic recording of cases of a designated disease or a group of diseases for a specific goal of monitoring or surveillance

location and/or time, providing each individual with a known (and often equal) chance of being selected

Question 7

What does active surveillance require?

Answer 7

sampling design and strategies with a large prevalence (<0.1% is not feasible, becomes more expensive with rare diseases)

Question 8

How are the imperfections of tests affected by prevalence?

Answer 8

imperfections play a stronger role as prevalence decreases

• decreased sensitivity = increased samples for detections
• decreased specificity = increased false positives

Question 9

What is design prevalence? What happens is levels are below this?

Answer 9

what level of diagnosis is expected in a population based on statistics of the specific location

difficult to find diagnosis - close to eradication

Question 10

What is passive surveillance? What does it depend on?

Answer 10

reporting of clinical or subclinical suspect cases to the health authorities by health care professionals at their discretion (wait for data to come to you)

willingness of professionals to secure the flow of data and awareness/knowledge of a particular disease among veterinary practitioners and producers/owners

Question 11

What are notifiable animal diseases? How do most countries rely on surveillance?

Answer 11

OIE-listed diseases that must be reported when diagnosed (USDA APHIS reportable diseases)

passive collection

Question 12

What is another way to describe passive surveillance? What is its main limitation?

Answer 12

secondary use of routinely collected data generated for another purpose - opportunistic in nature

inconsistency in the data collection for diseases —> relying on reports from others makes it difficult to compare MOSS data

Question 13

What is the difference between targeted and general surveillance?

Answer 13

TARGETED = surveillance in the context of targeting a disease using pathogen-specific diagnostic tests (PCR, ELISA, culture)

GENERAL = no targeted disease is tests using general diagnostic technique (clinical exam, necropsy, histology)

Question 14

When are targeted and general surveillance used?

Answer 14

TARGETED = targeting high-risk populations

GENERAL = detects new/emerging pathogens

Question 15

What are the major objectives of targeted and general surveillance?

Answer 15

TARGETED = detect cases of specific disease, describe endemic disease, demonstrate freedom from disease

GENERAL = detect emerging disease (no diagnostics available), describe endemic diseases

REMEMBER: objectives can change - BSE in US and Canada used targeted surveillance to demonstrate freedom, but found cases

Question 16

How do the types of surveillance systems overlap?

Answer 16

• ACTIVE TARGETED = serological survey to estimate prevalence of bovine brucellosis
• PASSIVE TARGETED = use milk processing data on bulk tank milk somatic cell counts to monitor mastitis control programs
• ACTIVE GENERAL = survey of veterinary practice records on patient clinical signs and disease
• PASSIVE GENERAL = veterinary investigations of farmer-reported disease events

(active + targeted; passive + general)

Question 17

What is risk-based surveillance? How is it done? Why does it tend to be cheaper compared to other ways of surveillance?

Answer 17

surveillance that is intentionally biased toward sub-populations that have higher risks of developing said disease, making there be a better probability of finding such disease

population is stratified according to known/hypothesized risk factors (strata not proportional to size)

increased efficiency of finding disease makes this way of surveillance cheaper

Question 18

What 3 risk factors can be used for risk-based surveillance?

Answer 18

1. causal factors - age group more susceptible to disease, farms with lower biosecurity
2. factors caused by disease - clinical signs appearing with disease
3. non-causal factors associated with disease - smaller farms with employees working in multiple sites

Question 19

How is syndromic surveillance done? Why is it so effective?

Answer 19

detection based on clinical signs associated with disease

allows possible early detection before laboratory confirmation

Question 20

What growing trend is starting to be used in surveillance? Where is this especially common?

Answer 20

participatory surveillance involving the public in the collection of disease information commonly on a digital format, since people of the street or at the farm level have a lot of information about certain diseases or syndromes

rural areas (Africa, Asia)

Question 21

What is the population coverage of MOSS? How do you decide upon the best coverage?

Answer 21

proportion of the population that is included in the surveillance system (census = every animal; sample = sub-population)

need to properly represent the target population - the rarer the disease, the more you need to sample

Question 22

What is the sensitivity of the MOSS? When is it applied?

Answer 22

probability that the MOSS will detect disease if it is there at a frequency greater or equal to the design prevalence, representing the level of confidence for disease detection if it were present in the target population at the design prevalence (DSe of individual tests)

disease detection or determining freedom from disease

Question 23

What should the MOSS specificity be?

Answer 23

conventionally assumed to be 100% - any positive will e investigated

• false positive = more sampling
• real positive = found diagnosis

Question 24

MOSS for determining freedom from disease:

Answer 24

Question 25

How has MOSS for freedom from disease been shifting lately?

Answer 25

historically, repeated separate surveys were conducted, but it is now shifting to ongoing surveillance

Question 26

How is probability of freedom from disease calculated?

Answer 26

comparing probability of introducing infection, biosecurity, and evidence supporting freedom (recent/historical tests)

Question 27

How is the weight of evidence supporting freedom from disease determined?

Answer 27

• number of animals tested
• accuracy of the test
• time