There are several types of risk assessment that fall under three broad categories:
All three categories provide useful information and your choice of assessment will depend on the speed and complexity you require from your assessment.
These are the simplest and quickest to do, but they can be rather subjective, which reduces their value. Every HACCP plan contains simple qualitative risk assessments in the HACCP worksheet.
For every hazard, an estimate of risk is made by inserting high, medium or low in answer to questions on the severity of the hazard and the likelihood of it occurring. A basic problem is that the three descriptors (high, medium, low) are often inadequate. For example, suppose the process step is retorting in fish canning and the hazard is Clostridium botulinum. Almost everyone will describe the severity of the hazard as high. But how likely is the hazard to occur? Most people will put low because billions of cans of fish are manufactured each year with no sign of the hazard. High severity and low likelihood - how would you link these to estimate risk?
|Process Step||Hazard||What Can Go Wrong||
|Severity of Hazard||Likelihood of Hazard Occurring|
|Hazard||Product||Severity of Hazard||Likelihood of Occurrence||Exposure in Diet||Link to Epidemiology||Risk Rank|
This assessment is based on factors which are linked with exposure assessment (likelihood of occurrence and exposure in the diet) plus one which is linked with hazard characterization (severity of hazard). If the hazard: product pairing has some linkage with epidemiology (it has caused food poisonings), this serves to remind you that there is some probability that it will happen again.
So, in Type 2 (above) we can make some assessment of exposure from our responses to likelihood of occurrence and exposure in the diet. Suppose we are considering ciguatera in two different populations, e.g. people in a Pacific island atoll community and the population of the United Kingdom. For the Pacific you would probably say the likelihood of occurrence of ciguatera is high. For the United Kingdom, you would probably say likelihood of occurrence is very low. There are strong links with epidemiology in atoll communities where the hazard is more or less accepted as an unavoidable fact of life; in contrast, ciguatera only rarely occurs in the United Kingdom from imported reef fish.
When all the information is brought together into a risk ranking you probably have a high or very high ranking for the Pacific and a low or very low ranking for the United Kingdom. The ranking will have value if you need a clear-cut answer in a relatively short time. To get the answer you will need to research the hazard and discover that it may have a cumulative effect but that it is rarely fatal. You will also look into epidemiology of the two target consumer groups - a few thousand atoll residents and 60 million United Kingdom residents. If you can find a recent review of ciguatera, especially one that is written in a risk assessment context, you could complete your research in a short time.
Another qualitative scheme for categorizing risk from seafoods has been developed by Huss, Reilly and Ben Embarek (2000) who ascribe pluses to hazard, then rank risks as "high" (four or more pluses) or "low" (less than four pluses). The scheme takes into account epidemiology (bad safety record) and then focuses on the process, searching for a critical control point (CCP) for each hazard and assessing possibilities for growth and death of microbial hazards.
|Risk Criteria||Raw Molluscan Shellfish||Canned Fish||Dried Fish|
|Possibility of Contamination||+||+||-|
|Growth of Pathogens on can||+||-||-|
|No terminal heating||+||-||+|
|Risk Category||High||Low||No Risk|
So, as shown in Type 3, molluscan shellfish, fish eaten raw, lightly-preserved fish and mildly heat-treated fish are considered "high" risk, while chilled/frozen fish and crustaceans, semi-preserved fish and heat-processed (canned) fish are considered "low" risk; dried and heavily salted fish are considered to have no risk.1.1.2 Semi-quantitative risk assessment
In qualitative risk assesment, we estimated risk according to subjective terms such as high, low or medium. In semi-quantitative risk assessment we obtain a numerical risk estimate based on a mixture of qualitative and quantitative data. To do this type of assessment you need much of the data that will be used in a full quantitative risk assessment. There is a great deal of work involved, but not as much as for a full quantitative risk assessment.
Ross and Sumner (2002) developed a simple spreadsheet tool to describe the risk that emerges from pathogens in products manufactured by typical processes (canning, chilling, cooking, etc). Table 1 lists risk criteria needed for a semi-quantitative risk assessment. These are simple questions and they can be answered qualitatively in terms such as "high" and "low". But the researchers found it possible to insert a quantitative basis to the answers. The tool is in Microsoft® Excel spreadsheet software and uses standard mathematical and logical functions. You can mouse-click your qualitative inputs, and the software will automatically convert them into quantities for calculations.
You must generate some data in order to answer the eleven questions in Table 1. To help you make your inputs as objective as possible, and to maintain transparency of the model, descriptions of the subjective descriptors are provided and many of the weighting factors are specified in the lists of descriptors. Alternatively, where the options provided do not accurately reflect the situation being modelled, you can enter a numerical value that is appropriate.
|Dose and Severity|
|1. Hazard Severity|
|Probability of Exposure|
|3. Frequency of Consumption|
|4. Proportion of Consuming|
|5. Size of Population|
|Probability of Infective Dose|
|6. Probability of Contamination|
|7. Effect of Process|
|8. Possibility of Recontamination|
|9. Post-process Control|
|10. Increase to Infective Dose|
|11. Effect of Treatment Before Eating|
The details behind the model can be read from the publication of Ross and Sumner (2002). Section 4 gives details about the tool, called Risk Ranger, and you can use it to work through some examples. The most robust risk estimates from Risk Ranger are a risk ranking (score from 0 to 100) and the number of illnesses per annum. This tool was used to provide a risk profile for the Australian seafood industry; later we will show you how its estimates were used to focus on those products and pathogens which required most attention from the industry.