Formal risk assessment is the process of systematic review of evidence that define or estimate a risk in the population. The purpose is to guide risk management (e.g. preventive and control measures). The concept of 'risk' is here defined as the [XXX hazard/impact * probability of occurrence.... to be completed..]
The differences with Rapid Risk Assessments are:
The scope of the assessment is the starting point. This could be the risk of introduction of a disease agent, or the risk of spread of a disease. It could cover threats to one sector (health) or many (e.g. agriculture, food, security). Once the scope is defined, the problem is formulated, with related objectives of the assessment (SMART). This will also clarify what sectors of society are affected by the problem.
Many hazards that are assessed are cross cutting through different sectors and disciplines in health. Therefore the team needs to reflect this multidisciplinary and multisectoral aspect. The group should be large enough to cover all areas, include representatives from health and other relevant sectors. Additional experts will be contacted to provide expert input.
When defining the risk of introduction of West Nile Virus in a country, then a first issue to address is estimating the probability of introduction of the virus in the population. This includes studying migratory routes of birds that could carry the virus and the presence of vectors (Aedes albopictus) in the country. Specifically the interest will be in the frequency of occurrence of specific migratory birds in the country (this can be informed via veterinarians and wild life societies) and the presence and future spread of the mosquito (this can be informed by environmental specialists and entomologists and in addition specialists in climate change).
Socio-economic factors (e.g. agricultural development, technological development, movement of people) also need to be taken into account
The scope of the risk assessment defines also the scope of the impact to describe: only health, or also other areas such as economics, travel, agriculture, security etc. The impact depends on various hazard factors.
Hazard factors for infectious agents are:
In addition, there will be several host factors that are relevant to describe:
Scenario tree modeling describes the chain of events that will lead to possible risks. This requires to describe a tree of events (each event step will be a relevant condition for the final risk). Then for each of these steps, the probability is assigned. Finally a sensitivity analysis is performed.
It is usually relevant for risk managers to have a visual representation of risks according to geographical region of a country (map). This will help to set priorities for risk reduction strategies. Risk maps can also aggregate information from different factors that are considered predictors of probability of an event.
Probability and impact need to be as much as possible fact and evidence based. Surveillance data (human, animal, environmental) are useful, as are specific surveys, published research. If information is missing from those sources, then expert opinion can be recruited to complement the required information.