Once an incident has been verified as being of potential public health concern, a rapid risk assessment is undertaken (usually within 24 to 48 hours) to evaluate the risk to human health. The risk to a  population from a communicable disease is dependent on the likelihood of transmission in the population  (probability) and the severity of disease (impact). The probability of an incident developing, and the impact if it  does, are based on both the nature of the infectious agent and details of the incident. This may be further influenced by context or the broad environment in which the incident occurs, including political, public, media  interest, perception of threat, and the acceptance of risk, which may vary between countries and cultures.

Rapid risk assessment is a core part of public health response and thus widely undertaken by public health  professionals. Formal systems which are used to grade evidence and recommendations, such as the systematic  methods used in evidence-based medicine, rely on published research evidence, and studies are graded according  to design and susceptibility to bias. However, as time and evidence are limited, a rapid risk assessment may need  to rely at least in part on specialist expert knowledge and these formal systems are not directly applicable. 

There are only a limited number of examples of a more systematic and transparent approach to rapid risk assessment in the literature including:

  • a qualitative method for assessing the risk from emerging infections in the UK (Morgan et al. 2009) using algorithms to consider the probability of an infection occurring in the UK population, its potential impact, and identifying gaps in knowledge or data;
  • a prioritisation approach to rank emerging zoonoses posing the greatest threat in the Netherlands, based on seven criteria (including probability of introduction, likelihood of transmission, economic damage, morbidity and mortality) to aid decision-making (http://www.rivm.nl/bibliotheek/rapporten/330214002.html);
  • a dynamic risk assessment model developed in the UK to assess the risk from an outbreak or incident, consisting of five attributes (severity, spread, confidence in the diagnosis, ease of intervention and the wider context in which events are occurring) rated over a 0 to 4 scale. During an outbreak, the dynamic risk assessment of each event occurring is used to inform management action at that time (http://hpzoneinfo.infact.com/HPZone/RiskAssessment/tabid/58/Default.aspx)

However, the same principles of transparency, explicitness, and reproducibility also apply to a rapid risk  assessment. For the rapid risk assessment of most infectious disease threats, observational data is often the only available and  obtainable source of information. Expert knowledge is also important if there is lack of time and evidence. In such  cases it is important to ‘unpack’ and make explicit the expert knowledge and distinguish between knowledge based  on good research, and experience and opinion-based knowledge. Serious attempts should be made to assess the  quality of the evidence, based on the source, design and quality of each study or piece of information. 

Uncertainties should be identified, clearly documented and communicated and the assessment updated in light of  new evidence over time. 

A rapid risk assessment includes the approach and tools required at each stage of the process: stage 0 is the  preparation stage; stage 1 is the collection of event information; stage 2 is the literature search and systematic  collection of information about the aetiological agent; stage 3 focuses on the extraction of evidence; stage 4  conducts an appraisal of the evidence; and stage 5 estimates the risk. Transparency and sharing of information is  essential at every stage. This document incorporates a step-by-step guide through each stage with examples and  checklists of the resources and evidence required. 

Advance preparation and planning saves time and is vital to ensure that potential threats are identified, assessed, and managed effectively. Ideally the following should be in place: evidence-based protocols and guidance for  responding to incidents, protocols for identifying sources of key information for rapid risk assessment, strategies  for literature searches, and lists of relevant contacts including named experts.

Rapid risk assessments of potential communicable disease threats can be complex and challenging as they must be  produced within a short time period when information is often limited and circumstances can evolve rapidly. The  rapid risk assessment methodology described in this document enables the structured identification of key  information using systematic appraisal of the best scientific evidence and/or specialist expert knowledge available at the time in order to provide a clear estimate of the scale of the health risk. This is important in not only communicating the potential magnitude of the risk in a systematic and transparent way, but allows documentation of evidence and gaps in knowledge at the time when the assessment is made.

References:

This text is the entire executive summary of a technical document published by ECDC:

Operational guidance on rapid risk assessment methodology. ECDC Technical Document. August 2011.