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Risk Ranking

Developing a food safety risk ranking metric for New Zealand

For regulators to make the best use of food safety resources, they need to identify, assess and compare the risks posed by various contaminant/food combinations and prioritise opportunities for reducing risks through targeted food safety initiatives. The process of comparing risks and ordering or grading them in some manner is known as risk ranking or comparative risk assessment.

The NZFSA Science Group has a goal of developing and applying a single metric of risk ranking that can be applied to both chemical and microbiological hazards and is applicable to the varied risk ranking needs of the NZFSA. This is an ongoing, iterative process as methods and experience develops involving several projects carried out by ESR.

The objective of the work is to investigate risk ranking as a process, without being restricted to actual ranking of food safety issues. Existing models and practical examples of risk ranking exercises, principally from overseas, were reviewed. The following reports provide a basis for development of a consultative approach to ranking of risks associated with hazards in New Zealand consumed foods. This is regarded as an ongoing project by NZFSA.

Ranking Food Safety Risks: A Discussion Document [PDF 235 KB]

Initially a scientifically-based for ranking food safety risks was developed. The following steps were identified:

• Define and categorise the risk to be ranked
• Identify the risk attributes (criteria) that should be considered
• Describe the risks in terms of the attributes
• Perform the risk ranking
• Describe the issues identified and the resulting ranking.

The categorisation of risks is covered by food/hazard combinations. The criteria for ranking include:

• Public health (incidence of illness apportioned to the food of interest)
• Severity (morbidity, mortality)
• Exposure (food consumption, hazard prevalence)
• Uncertainty (quality of data)
• Topicality (emerging hazards, changes in existing hazards).

Ranking Food Safety Risks: A Prototype Methodology [PDF 391 KB]

The NZFSA Science Group developed criteria for ranking based on

• Public health
• Severity
• Uncertainty.

Due to uncertainty in describing the food/hazard (microbiological) combinations in terms of these criteria (particularly apportionment), an expert consultation was held to describe the risks in terms of the attributes. The following were examined:

• Apportionment of total disease incidence due to transmission of foods in general
• Apportionment of total disease incidence due to transmission in the specific foods identified
• Severity
• Associated issues, such as definition of 'foodborne'.

The apportionment and severity estimates were combined to give a final ranking,

Resulting from the consultation alterations to the risk ranking process was proposed:

• Define and categories the food/hazard combinations whose risks are ranked
• Assemble available scientific data related to the attributes incidence and severity
• Describe the risks in terms of the attributes on the basis of expert consultation
• Combine scientific data and expert consultation to produce the risk ranking
• Describe the issues identified and the resulting rankings.

Ranking Food Safety Risks: Development of NZFSA Policy 2004 - 2005 [PDF 238 KB]

The objective of this work was to develop a single metric to describe the burden of disease by combining information about severity and incidence.

Alternatives derive from economic evaluations of health care are:

• Cost analysis: costs in monetary terms
• Cost-effectiveness analysis: costs in monetary terms, consequences measured in natural units
• Cost-unity analysis: costs in monetary units, consequences measured in healthy year (quality adjusted life years (QALYs) or disability adjusted life years (DALYs)
• Cost-benefit analysis: costs in monetary units, consequences in monetary units.

The DALY measure is the preferred single metric.

Risk Ranking: Development of a Single Metric for Risk Ranking by the NZFSA [PDF  92.6 KB]
Risk Ranking: Estimates of the Burden of Foodborne Disease for New Zealand [PDF 641 KB]

Disability Adjusted Life Year (DALY) estimates were developed for six potentially foodbone diseases resulting in the following ranking:

• Campylobacteriois
• Listeriosis (invasive, perinatal and non-perinatal)
• Norovirus infection
• Salmonellosis
• Yersiniosis
• STEC infection

The estimates associated with different disease vary widely in their degree of associated uncertainty.

The DALY approach provides a useful mechanism for assimilating a huge amount of information on infectious intestinal disease, that would not otherwise be comparable, to produce a single metric suitable as an input to risk prioritisation.

Risk Ranking: Estimates of the Cost of Foodborne Disease for New Zealand [PDF 247 KB]

Estimates for the direct and indirect economic burden of the six previously studied diseases were prepared. Cost of illness estimate is an alternative metric to the DALY burden of illness for comparing the impact of food hazards. The estimates represent a combination of disease incidence with unit costs.

The total estimated cost to New Zealand society due to foodborne transmission of disease directly or subsequently due to Campylobacter, Salmonlle, Listeria momocytogenes,shig-toxin producing Escherischia coli, Yersinia enterocolitica, and Norovirus is estimated to be c$86 million, with approximately 90% of the cost due to lost productivity.

Risk ranking: DALY Estimates for Selected Foodborne Diseases in New Zealand using Revised Dutch Disability Weights [PDF 360 KB]

The approach used in developing DALY estimates for New Zealand was strongly guided by estimates prepared for the Netherlands. Since preparation of those New Zealand estimates, further Dutch work examining disability weights has become available. These new disability weights include consideration of the duration of illness so that it does not need to be part of the calculation. The participant surveys used to develop the disability weights also included a relevance criterion, where minimal disease might be excluded from the burden estimate. This current report provides revised estimates for New Zealand using the new research from the Netherlands.

While the revised disability weights resulted in some changes in the magnitude of individual DALY estimates, they had little impact on the relative ranking of the diseases considered.

Updated 24 July 2009