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What is surveillance?
systematic collection, analysis, and interp of data and dissemination of information to those who should take action
Contrast surveillance, monitoring, and screening.
- surveillance: data collection with the objective of intervening to change the outcome in a defined population
- monitoring: surveillance without a threshold
- screening: testing to ID individuals with infection or disease to protect public health; measurement of prevalence in screened populations
The critical goal of surveillance is to...
control and/or prevent diseases with timely intervention
What is the objective of early detection?
identify dz rapidly before significant spread
For early detection, the surveillance system should... (3)
- be continuous
- have comprehensive coverage of the population
- be sensitive (negative means they really don't have the dz) with very low design prevalence
What is the objective of demonstration of freedom (of dz)?
provide proof of no disease (for trade support, stopping control measures, ad hoc or risk-based testing instead of continuous, etc)
Surveillance to demonstrate freedom of dz: (3)
- does not need to be continuous, but may be ad hoc or intermittent
- can use risk-based sampling
- uses a higher design prevalence than early detection
What are the purposes of surveillance in apparently non-infected populations and infected populations?
- absent of dz: early detection or demonstration of freedom
- dz present: case finding, measuring levels of dz
What is the objective of case finding?
ID infected animals, flocks, or herd during a control program
Case finding surveillance should... (4)
- use comprehensive coverage of the population, with a focus on high risk pops
- parts of the population
- be ongoing
- have good individual herd or animal sensitivity
What is the objective of surveillance to measure levels of dz?
to detect changes in the level of disease (esp increases)
Surveillance to measure levels of dz: (3)
- does not need to be continuous but can be ad hoc or periodic
- should be based on representative sampling to avoid bias
- should use a big enough sample size to give adequate precision
Effectiveness of a surveillance program is dependent upon... (3)
- quality of sampling
- amount of surveillance being done
- distribution of sampling
What are the principals to meet the surveillance objectives? (3)
- timeliness ( how rapidly the system can produce information (ongoing, regular, ad hoc)
- population coverage
Contrast active and passive surveillance.
- Active: utilizing samples or observations collected specifically for use by the surveillance program; needed for the rare or hard to detect dz
- Passive: utilizing samples/ observations collected primarily for another purpose; reliant upon health care providers/labs to report cases of dz
What are the advantages and disadvantages of passive surveillance?
- advantage is efficiency, less resources needed
- disadvantage is possibility of incomplete data/ underreporting
What are the advantages and disadvantages of active surveillance?
- advantage is high level of completeness, better for rare diseases
- disadvantage is that it's much more expensive and needs more resources
What are 2 types of passive surveillance and of active surveillance?
- Passive: case-based (animals and people), syndromic (people)
- Active: Biosensor (environment), pathogen screening (animals)
Describe case-based surveillance.
- List of reportable diseases
- timeliness is within days to week
- representativeness: required in all states
- sensitivity: predetermined case definitions
Describe syndromic surveillance.
- signs symptoms indicative of a dz/ disorder are reported
- timeliness is near real time
- representativeness: entities willing/ able to participate
- high sensitivity, low specificity; less severe cases may not be identified
Describe the Biosensor method of active surveillance.
- monitors samples from the environment
- timeliness: 12-36 hours after agent release
- representativeness: discrete locations only
- sensitivity: does not confirm human exposure
- used to monitor for bioterrorism
Procedure by which some members of a given population are selected and measured as representatives of the entire population.
Representative sampling: prevalence in population ______ prevalence in sample.
Risk-based sampling: prevalence in population ______ prevalence in sample.
Biased sampling: prevalence in population ______ prevalence in sample.
What are the steps of sampling? (5)
- 1. define objectives
- 2. ID target population
- 3. determine required precision
- 4. decide sampling units (group, herd, individuals, regions, etc)
- 5. develop sampling frame (list of sampling units from which sample will be drawn)
Contrast non-probability and probability sampling.
- non-probability: convenience sampling
- probability: simple random, systematic random, stratified random, cluster, multistage sampling
Describe simple random sampling.
- selects a fixed percentage of the sampling frame using a formal random process
- known probability that an individual sampling unit will be selected from the sampling frame
What are specific diseases that we have surveillance programs for? (6)
- classic swine fever (CSF)
- avian influenza