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Enhanced Surveillance for Avian Influenza and Other Disease Risks. Professor Roger Morris and colleagues Massey University EpiCentre Palmerston North New Zealand. Why do surveillance?. To provide evidence that a disease is absent
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Enhanced Surveillance for Avian Influenza and Other Disease Risks Professor Roger Morris and colleagues Massey University EpiCentre Palmerston North New Zealand
Why do surveillance? • To provide evidence that a disease is absent • To reduce the risk of taking the wrong disease control action • And the risk of failing to act when necessary to do so • We are developing economic methods to decide how to invest each dollar of surveillance money most wisely
Adapting surveillance to new needs • Surveillance systems have not adapted fast enough to changing requirements • Need to make surveillance more “risk-based” • Diseases form a limited number of epitypes – require similar surveillance strategies • Scanning and targeted surveillance • Design better systems to collect and analyse surveillance data so that it is used effectively for making wise decisions • Make outputs more current and targeted to the various users of the data
Risk-based surveillance • Develop surveillance portfolio • Balanced combination of techniques • Scanning surveillance – broad assessment • Targeted surveillance – answer specific questions about a disease • Use information on risk factors for a disease to help allocate effort • Develop risk landscape to guide decisions on surveillance strategy – surveillance data lowers the risk mountains to a flat plain
The epidemiological toolbox • Data gathering which can yield a valid and insightful assessment of field disease situation • Analytical tools which can achieve this • Modelling tools to evaluate and predict • Surveillance portfolio to guide decisions • Integrating information system to make it happen
Disease mapping for surveillance • GIS software now very important to interpret patterns of disease • Especially if used jointly with other epidemiological methods • Allows more cost-effective selection of samples to include in surveillance system • Now have powerful analytical techniques to interpret spatial patterns and relate to risk factors
Data gathering methods • Expanding range of methods used • Participatory methods • Syndromic surveillance • Field investigation strategies • Molecular epidemiology linked with other tools • Laboratory data should be tightly targeted • Integrate laboratory and field methods • Multiple imperfect methods better than single perfect source
Farmer surveys – simple but effective 300 duck farmers in southern Vietnam interviewed in two weeks Are ducks really the problem here? – 98% have more than 80% of ducks vaccinated But 60% of these people have less than 80% of chickens vaccinated Ducks are not moved nearly as far as senior vets thought
AI investigation in villages and markets • Investigating low path viruses as well as H5N1 can help give a better understanding of methods of spread of AI viruses, and how to control them • In Hong Kong markets, spread involved drinking water, minor poultry species (quail), pet rooster • Spread of H5N1 to local farms was from markets, not the other way • Molecular epidemiology showed that there were four incursions not one, with different spread
Studies in Vietnam • Vietnam has had a lot of outbreaks, has made good progress in reducing the number per year • Analysed spatial and temporal pattern of poultry outbreaks 2004-7, especially in two deltas • Association between human and poultry cases • Role of ducks and other birds in AI spread, factors influencing disease occurrence • Will use this information to develop a targeted surveillance system, with computer tools to support it
Poisson regression of risk areas • Examined pattern of outbreaks 2003-4 using a grid overlaid on country • Areas with over 66% of land irrigated at much higher risk of outbreaks • Areas below 250m altitude at increased risk • Other factors examined were not influential • Potential use of satellite imaging to guide surveillance investment
How should we investigate AI? • Sero-monitoring has only limited value in a vaccinated population • Is NOT a disease surveillance method in this situation, only checks vaccine coverage • Want 80%+ birds protected for AI • To test whether protection level adequate, test 250 animals – for any size population • So design sampling plan to test that vaccination program is working in different sectors (3, 4), production systems and regions of the country
Disease surveillance • Want to determine distribution of infection and transmission patterns • PCR is a valuable technique, but only useful if use virus isolation as well, to confirm that virus is circulating and check PCR accuracy • PCR should always give some positives, even if no infection present! • Virus isolation and molecular strain investigation most useful investigation method to understand virus transmission
Investigating AI • Focus should be on understanding how infection is transmitted and maintained, then monitoring it • Main emphasis should be on investigating sector 3 and sector 4 flocks, live bird markets • Need epidemiological investigation strategy to answer key questions through good design • If you ask the right questions, spend far less on testing, but get more useful results • Use modern analytical methods
Data Analysis • Many powerful analytical methods now available • Do not need perfect data provided that study design is sound • Carefully designed intensive epidemiological investigations to examine risk factors are far more useful than large-scale sampling done without collecting risk factor data • Then can use modelling and other techniques to test various explanations of the disease pattern
Number of cattle moved OUT of departments for finishing: Jan - Mar Social network analysis can be used to investigate disease spread pathways Grey lines indicate movement of > 1000 head for 3-month period. Symbols proportional to number of cattle moved.
Spatial modelling of disease • Valuable method of assessing possible causes • Valuable for evaluating control options • We use generic spatial models which can be given the “profile” of any known (or new) disease • Modelled foot and mouth disease epidemic in 2001 for Britain, modelling avian influenza with same model
Monitoring control program results • Need baseline data on the situation before control activities are started • Need to use a monitoring system which accurately measures change in prevalence of disease and/or infection • Need to gather information which will allow you to detect and respond to weaknesses in the program
Animal health information system • Use an approach which suits the needs of the country, start simple but with development plan • It must allow data analysis from the start, and be able to advance as the country’s needs change • Should include both disease control and surveillance • Ability to map disease data should be seen as an important feature which must be available, though it may not be used at first
Developing a surveillance portfolio • Retirement planning: • Invest in multiple assets to spread your risk • Evaluate performance by expected $$ return • Consider variation around $$ return • Surveillance assets: Invest in multiple surveillance techniques to give balanced picture Can use points per sample or investigation, instead of $$ Each component of surveillance program has a different cost and different number of points achieved by particular test or investigation Applied to BSE and Trichinella, adapting to other diseases Risk-based sampling can give better assurance of disease state
Risk-based sampling for exotic disease Comparison of the number of tests allocated per SA and the maximum possible disease prevalence in ewe flocks (α = 0.05) when distributing samples using portfolio theory (PT) and proportional allocation (PA)
Risk assessment Activate P1 P2 P3
Feedback to participants • A major issue in achieving effective surveillance is getting cooperation from data providers • Essential for completeness, and to minimise bias • Feedback is most important stimulus to continuing cooperation
Conclusion • We need to be ready to face and solve new disease challenges • Effective surveillance is the key to quick detection and effective control • Surveillance needs multiple sources of information, and smart tools for interpretation • Need integrated surveillance and response strategy if we are to control future diseases successfully, and a toolbox of techniques to quickly determine what is going on