Risk Assessment in the context of Bio-risk Management

Transcription

1 Risk Assessment in the context of Bio-risk Management 1

2 Some preliminary information 2

3 Hazard 3

4 Hazard It is a qualitative notion It is a biological, chemical or physical agent that may have adverse health effects 4

5 Risk 5

6 Risk Risk is a a fundamentally quantitative notion Risk may be expressed qualitatively (in words) e.g. high risk, low risk, negligible risk, but it remains a nonnumerical way to quantify the likelihood of a damage 6

7 Risk Risk has two components: the probability of occurrence of an unwanted effect the magnitude of the unwanted effect when it occurs 7

8 Risk analysis 8

9 Risk is never zero 9

10 Risk is never zero nevertheless, we can decrease it. It is possible to reduce either the probability of an unwanted event or the magnitude of the unwanted event by the adoption of risk-mitigation measures Up to what level of reduction? 10

11 Risk is never zero Acceptable risk: No level of risk can be considered as acceptable by definition No level of risk can be considered as scientifically acceptable Acceptable risk is that level of risk that a (democratic) society as a whole is willing to accept 11

12 Risk is never zero willing to accept, taking into consideration that risk-mitigation measures have a cost available resources are inherently limited several hazards compete with one another for the allocation of the available resources 12

13 Risk is never zero the establishment of an acceptable level of risk (*), like any other decision on resource allocation, is the result of a political mediation (*) ALOP: Appropriate Level of Protection 13

14 Risk is never zero Elements to consider: quantification of the risk (probability and magnitude, that is prevalence and level of contamination) cost of each potential risk mitigation measure quantification of the reduction of risk achievable with each mitigation measure or set thereof 14

15 Components of risk analysis and steps of a risk assessment according to the OIE Terrestrial Animal Health Code 15

16 Covello and Merkhofer model 16

17 Components of the Covello and Merkhofer model The hazard identification involves identifying the pathogenic agents which could potentially produce adverse consequences when released in an environment. Hazard identification is a categorization step, identifying biological agents dichotomously as hazards or not. 17

18 Hazard Identification 18

19 Hazard Identification 19

20 Hazard Identification 20

21 Hazard Identification 21

22 Risk Assessment Risk assessment for the release of a pathogen from a lab is a Quantitative Risk Assessment 22

23 Final outputs of the risk assessment A quantitative risk assessment is performed using mathematical models or computer simulations See example with the testing of a sample from a sheep flock 23

24 Final outputs of the risk assessment For a quantitative assessment, the final outputs may include: estimated numbers of herds, flocks, animals or people likely to experience health impacts of various degrees of severity over time; probability distributions, confidence intervals, and other means for expressing the uncertainties in these estimates; description of the variance of all model inputs; a sensitivity analysis to rank the inputs as to their contribution to the variance of the risk estimation output; analysis of the dependence and correlation between model inputs. 24

25 Final output of the risk assessment We have said that the risk has two components: magnitude of the damage and probability How do we represent the estimated numbers of herds, flocks, animals or people likely to experience health impacts AND their probability? 25

26 How are the two components represented? Risk curves 26

27 Let s put the Risk Assessment in the context of Bio-risk Management 27

28 The National Bio and Agro Defense Facility (NBAF) The current research facility at Plum Island Animal Disease Center (PIADC) in New York, the primary animal disease research facility since 1954, is getting very old. In 2009, Manhattan, Kansas was selected as the site for the new National Bio and Agro Defense Facility (NBAF) to replace PIADC. 28

29 The National Bio and Agro Defense Facility (NBAF) However, the US government would not allow funds to be made available for construction of NBAF until:...a site-specific bio-safety and biosecurity mitigation risk assessment, which includes an integrated set of analyses using plume modeling and epidemiologic impact modeling..., and the results of the National Academy of Sciences review of the risk assessment... 29

30 The National Bio and Agro Defense Facility (NBAF) We will use the risk assessment performed for the NBAF as a model for the execution of a risk assessment in the context of bio-risk management 30

31 The NBAF Site-Specific Risk Assessment (SSRA) FMD 31

32 How can a pathogen be released from a lab? 32

33 The NBAF Site-Specific Risk Assessment (SSRA) Historically described pathways for pathogen release from a Foreign Animal Disease Center: the example of the FMD outbreak at Pirbright in 2007: leaking drainage pipes was determined to be the likely cause 33

34 The NBAF Site-Specific Risk Assessment (SSRA) Historically described pathways for pathogen release from a Foreign Animal Disease Center: the example of Plum Island in

35 Date The NBAF Site-Specific Risk Assessment (SSRA) Internal Releases of Foot-and-Mouth Virus at Plum Island, Sept Apr.12, 1974 Aug. 21, 1980 Feb. 24, 1981 May 26, 1987 June 24, 2004 Probable cause An air leak in a door gasket Leaks in the walls combined with a power failure Mechanical transfer by a laboratory worker Cross-contamination from an unknown source Fluids leaking during transport of carcasses Cross-contamination from an unknown source 35

36 The scenarios for pathogen release considered in the NBAF-SSRA 36

37 The scenarios for pathogen release considered in the NBAF-SSRA 37

38 Release assessment: Scenario Tree For each scenario, the relevant scenario tree is developed The scenario tree is the conceptual description of the various steps through which a given event can result in an adverse outcome or not, with the specification of the probabilities involved at each branch of the tree 38

39 Release assessment: Scenario Tree 39

40 The NBAF Site-Specific Risk Assessment (SSRA) 40

41 NBAF-SSRA Exposure assessment For each release event from the NBAF that causes a Foot-and-Mouth Disease (FMD) infection at a livestock premises, the consequences of that outbreak must be calculated to understand overall risk 41

42 NBAF-SSRA Exposure assessment Determine the probability that an outbreak starts in various possible locations given release quantity and transport pathways; Estimate the extent and duration of the possible FMD outbreaks in Kansas; Determine the probability that an outbreak would spread from Kansas to other states; Estimate the extent and duration of possible FMD outbreaks in states other than Kansas; and Determine overall risk by combining impact and probability of outbreaks occurring across the region for each release amount and transport pathway. 42

43 Exposure assessment Outbreak Starting Locations Determine the probability that an outbreak starts in various possible locations given release quantity and transport pathways, i.e. determining outbreak starting locations (the impact and extent of the outbreak depends significantly on the type of livestock initially infected and the connectedness of the infected premises with the livestock industry as a whole): Given the amount of pathogen released and the means by which the infectious material is transported in the environment (calculated from Scenario and transport pathway and scenario tree) The risk of infection at any premises can be calculated. The method to calculate this risk is specific to an event pathway 43

44 Exposure assessment Outbreak Starting Locations Three pathways are considered: Infectious aerosol releases; Contaminated personnel or fomites; Release of contaminated waste. I m not going to elaborate further on the modelling of these three pathways. What is necessary to say is that the methods estimate the probability that at least one animal in the receiving holding develop FMD infection, given the dose of virus to which all animals at that holding are exposed and a Probit dose-response curve. 44

45 Exposure assessment Spread Of The Infection Next step in the exposure assessment is the modelling of the spread of the infection from the outbreak starting locations, that is: Estimate the extent and duration of the possible FMD outbreaks in Kansas; Determine the probability that an outbreak would spread from Kansas to other states; Estimate the extent and duration of possible FMD outbreaks in states other than Kansas; and Determine overall risk by combining impact and probability of outbreaks occurring across the region for each release amount and transport pathway. 45

46 Exposure assessment Spread Of The Infection In Europe or Japan this phase of the modelling would be a straightforward endeavor. In Europe we have the complete and updated list of holdings where farm animals are kept, with their geolocation and the type of animals kept Moreover, all animal movements (for trade or other reasons) are recorded with the indication of the number of animals moved their destination and the date of movement 46

47 Exposure assessment Spread Of The Infection The modelling of the spread of infection in Europe can be done very precisely using two tools: the description of the trade sub-network originating from each Outbreak starting location a simulation using a state transition model to describe the dynamics of the possible infection in each farm of the sub-network 47

48 The description of the network 48

49 The stochastic state transition model 49

50 Spread of the infection This approach has been assessed as a tool to optimize the farm visits by the veterinary services in case of a real world outbreak and has been used as a tool to perform the tracing of infections in a outbreak 50

51 Spread of the infection This modelling approach is very precise and can provide accurate estimations of the outcome of a virus release from the NBAF and of its costs Unfortunately it is not applicable outside the EU and Japan, that is in most of the world 51

52 Spread of the disease Outside the EU and Japan, only approximate estimations of the spread of the disease are achievable, by using spread models that make the best use of the available data 52

53 The NAADSM The North American Animal Disease Spread Model (NAADSM) is a spatial, stochastic, state-transition simulation model that simulates highly contagious animal diseases. The NAADSM is the model used in the NBAF-SSRA to assess the disease spread after a release of FMD virus from the NBAF 53

54 The NAADSM The NAADSM framework requires extensive parameterization including information on animal population (e.g., location, production type, size of herd), disease manifestation (e.g., latently infected), disease transmission (e.g., direct, indirect, and aerosol), disease detection, surveillance, and control (e.g., animal movements, traceability, and vaccination). 54

55 The NAADSM The data used to develop NAADSM parameters came from a variety of sources including government reports, open source literature and interviews with subject matter experts (SMEs). In NAADSM, farms are grouped by production type. All farms within a production type share characteristics due to similar livestock management practices and the presence of the same species of animal. 55

56 The NAADSM Production Types Used for the SSRA Epidemiological Model were: Cow-Calf Dairy Feedlot (Large) / (Small) Swine (Large) / (Small) Goat Sheep Beef backyard and small scale Swine backyard and small scale Small ruminants backyard and small scale 56

57 The NAADSM Susceptible Animal Populations: Survey of All Animals within 6.2 Miles (=10 km) of the NBAF including the location (lat and lon), herd size and production type of every herd in the region. data from Concentrated Animal Feeding Operation (CAFO) permits, issued by EPA for wastewater management. CAFOs provide a comprehensive list of all large animal livestock operations in each state. Generally, records included location, production type, and number of animals... 57

58 The NAADSM Susceptible Animal Populations:... data purchased from the Dunn & Bradstreet (D&B) business database. D&B is a company that compiles information about the revenue generating activities and geographical locations of corporations and businesses. D&B records provide location and production type information, but number of animals had to be extrapolated

59 The NAADSM Susceptible Animal Populations:... LLNL Animal Population Dataset. LLNL developed a dataset of farms (including production type, size and location) computed from data in the NASS 2007 Agricultural Survey. This dataset was used to help account for all the small and medium sized facilities not identified through CAFO permit datasets, D&B datasets, and surveys. Duplications of farms in the datasets used were removed using pre-defined rules. 59

60 The NAADSM Intra-herd spread: it was assessed using the stochastic state transition model The result of these simulations was the probability distribution of the herd-level disease phase durations, and the proportion of animals infected in a herd, expressed by the within-unit prevalence function 60

61 The herd-level disease phase distributions 61

62 The proportion of animals infected in a herd 62

63 The NBAF Site-Specific Risk Assessment (SSRA) 63

64 Economic analysis 64

65 Economic analysis The NBAF-SSRA also included an economical analysis I don t go into the details of the economic analysis I will just show one example of the results of the economical analysis 65

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