3.2. Risk assessment

Risk assessment is the rational application of safety principles to available options for handling hazardous materials. The following characteristics are considered when evaluating a potential pathogen:

• the agent’s biological and physical nature;
• the sources likely to harbor the agent;
• the h;
• the procedures that may disseminate the agent;
• the best method to effectively inactivate the agent.

The biological nature of pathogens determined their distribution into risk groups.

Risk groups of pathogens

Microorganisms that are human pathogens can be categorized into risk groups (RG) based onthe transmissibility, invasiveness, virulence (i.e., ability to cause disease), and the lethality of thespecific pathogen. Risk groupings of infectious agents (RG1 through RG4) approximatelycorrespond to biosafety levels (BSL1 through BSL4), which describe containment practices,safety equipment, and facility design features recommended for safe handling of thesemicroorganisms.

Beginning with RG1 agents, which are nonpathogenic for healthy human adults, the schemeascends in order of increasing hazard to RG4.

RISK GROUP 1 agents are not associated with disease in healthy adult humans. Examples: E.coli K-12, Saccharomyces cerevisiae.

RISK GROUP 2 agents are associated with human disease that is rarely serious and for whichpreventive or therapeutic interventions are often available. Examples: enteropathogenic E. colistrains, Salmonella, L. monocytogenes, Cryptosporidium, and Staphylococcus aureus.

RISK GROUP 3 agents are associated with serious or lethal human disease for whichpreventive or therapeutic interventions may be available (high individual risk but lowcommunity risk). Examples: human immunodeficiency virus, Brucella abortus, Mycobacteriumtuberculosis.

RISK GROUP 4 agents are likely to cause serious or lethal human disease for whichpreventive or therapeutic interventions are not usually available (high individual risk and highcommunity risk). Examples: Ebola virus, Cercopithecine herpesvirus 1 (Herpes B or Monkey Bvirus).

Consideration of the risk group assignment, however, merely is a starting point for thecomprehensive risk assessment. Further attention must be given to the circumstances, such asthe planned procedures and the available safety equipment. Then, the recommendedprecautions may be increased or decreased relative to those based solely on the risk groupassignment and adjusted to reflect the specific situation in which the pathogen will be used.Microorganisms in RG1 require use of standard basic biological laboratory facilities andmicrobiological practices, whereas those in RG4 require maximum containment facilities andpractices. Some of the agents likely to be handled experimentally at UW-Madison are RG2 orRG3 pathogens; designated as moderate and high hazard, respectively. These agents typicallyrequire more sophisticated engineering controls (e.g., facilities and equipment) than are availablein standard laboratories, as well as special handling and decontamination procedures. Consideration also is extended to microorganisms that cause diseases in animals and/or plants,which are not categorized into risk groups as are human pathogens. The desired containmentfor animal and plant pathogens is based on the severity of the disease and its ability todisseminate and become established in the local environment.

The progression from invasion to infection to disease following contact with an infectiousagent depends upon the dose, route of transmission, invasive characteristics of the agent,virulence and resistance of the exposed host. Not all contacts result in infection and even fewerdevelop into clinical disease. Even when disease occurs, its severity can vary considerably.Attenuated strains should be handled with the same precautions as the virulent strain unless thereduced pathogenicity is well documented and is irreversible. Viral vectors, even if renderedreplication defective, still may pose a threat of recombination with wild-type strains and/orunintentional delivery of their foreign genes. It is prudent to assume virulence.

Which human pathogens are harbored by plant products?

Four priority pathogens have been identified by the regulatory agencies as the initial focus of foodborne illness source attribution work: Salmonella, E. coli O157:H7, Listeria monocytogenes, and Campylobacter. Furthermore, surveys of plant products have shown the potential for high-risk plant productsto be also contaminated with L. monocytogenes, Aeromonas spp., E. coli,B. cereus, C. botulinum, andSalmonella, when they are consumed raw.Contamination of fresh cut fruit and vegetables,as discussed in the previous section, can occur during growth, harvest orprocessing and storage of harvest and packing in a modified atmosphere.

The presented risk assessment will review the hazards associated with food businessesregulated under the food safety schemes of Food Regulation andincludes plant products, such as fresh cut fruits and vegetables, unpasteurized juice, andvegetables in oil. Risk assessmentforms part of an overall process, called risk analysis. Risk analysis isused by governments and industry to assess, manage, and communicate the riskassociated with particular food or food groups and in turn aims to reduce the risk of foodborne illness.

The Codex Alimentarius Commission (CAC) divides riskanalysis into three components:

• Risk assessment – a process by which the potential risk posed by food safetyhazard(s) is determined;

•Risk management – the process of determining alternatives to control thehazards identified in the risk assessment; and

• Risk communication – the exchange of information on risk and riskmanagement amongst interested parties.

CAC (1999) has identified four components of risk assessment:

• Hazard identification – the process of identifying potential hazards associatedwith the food.

• Exposure assessment – an estimation of the potential human exposure to thehazard,which includes the use of data such as the occurrence in a particular foodand/or potential consumption rates of the food. Exposure assessment can be defined as the set of circumstances that influence the extent of exposure.

• Hazard characterisation – the evaluation of the potential illness associatedwith the hazard.

• Risk characterisation – the process of determining the probability ofoccurrence and severity of the adverse health effects based on theinformation collected in the hazard identification, exposure assessment andhazard characterisation. Risk characterization can be viewed as a “quantitative measurement” of the probability of adverse effects under defined conditions of exposure. Some authors, when evaluating the effect of plant pathogens, also add the step of dose-response evaluation, which involvesdetermination of the relationship between the magnitude of exposure and probability of the adverse effect.

 

3.2.1. Hazard identification

Microbiological hazard was designated for six products (Table 1) with high risk of contamination with pathogens. The food safety scheme was developed to introduce minimum regulatory requirements for businesses producing high-risk plant products, and to implement control measures to minimize the risks from the microbiological hazards associated with these products.

Table 1. Microbiological hazards associated with plant products

Plant product	High risk ranking	Medium risk ranking
Fresh cut vegetables – may be consumed raw	Pathogenic E. coli
	Salmonella serovars
	L. monocytogenes
Fresh cut vegetables – chilled, MAP or extended shelf life	L. monocytogenes
	C. botulinum
Vegetables in oil	C. botulinum
Seed sprouts	Pathogenic E. coli	B. cereus
	Salmonella serovars	L. monocytogenes
Fresh cut fruit	Pathogenic E. coli	Cryptosporidium parvum
	Salmonella serovars	Enteric viruses
	L. monocytogenes
Fruit juice / drink (unpasteurized)	Salmonella serovars
	Pathogenic E. coli
Adapted from FSA (2000a)

 

Fresh cut vegetablesFresh cut fruits and vegetables are raw agricultural products that have been processed by means of washing, trimming, cutting or slicing to be made ready for consumption. Contamination of vegetables may occur during growth, harvest or processing. Under certain conditions microorganisms can also become internalized within the vegetables. Conditions that promote internalisation of microorganisms include damage to the natural structure (e.g. punctures, stem scars, cuts, and splits) and placing warm produce into cooler, contaminated wash water.These foods have a high potential risk due to the contamination with pathogenic E. coli, Salmonella serovars and L. monocytogenes. The actual process of cutting and/or removing the protective outer surfaces of the plants may increase the potential for pathogenic bacteria to survive and/or grow. Many vegetable products do not undergo a kill step that will completely eliminate pathogens; however, measures such as sanitising washes may be used to reduce microbial contamination with pathogens.

Many fresh cut vegetables are packaged using MAP and refrigerated to extend the shelf life. This form of processing may lead to an increased risk from pathogens such as L. monocytogenes and psychrotrophic strains of C. botulinum by enhancing the conditions for their survival and allowing additional time for growth. MAP products may become fully anaerobic if the plant tissue is actively respiring and uses up all the oxygen. As any competition from aerobic spoilage organisms is inhibited, this may increase the opportunity for anaerobic or facultative anaerobic pathogens to grow.

Fresh cut fruit

Fresh fruit are normally perceived as low risk foods, as they tend to have a thicker protective skin than most vegetables and most are harvested from trees or bushes. The notable exceptions are melons and strawberries, which are considered higher risk because they grow close to the ground and their surfaces may become contaminated with soil.

Contamination of fruit may occur at any point from growing (soil, fertilisation, irrigation water, and animal/bird waste), through harvesting and processing (including washing), to distribution, marketing, and consumption. Many microbial pathogens cannot survive or grow on most fruit due to the low pH environment. However, melons and strawberries have relatively high pH, which makes them more likely to be a food safety hazard. In addition, the skin of rockmelon tends to be porous, which may allow the penetration of pathogens and agricultural chemicals into the fruit. Melons are often dipped in a sanitizing solution after harvest (FSA, 2000a).

Fresh cut fruits may be value added by peeling, chopping, slicing, and packaging. Many fresh cut fruit are packaged using MAP and refrigerated to extend the shelf life. With additional time, this can lead to an increased risk from pathogens that are adapted to the acidic environment of fruit and are able to survive and grow in these foods.

A range of bacterial (E. coli, Salmonella serovars, and L. monocytogenes) and viral pathogens, and enteric parasites(Cryptosporidium parvum) have been identified as being of concern in fresh cut fruit. The actual process of cutting and/or removing protective outer surfaces of the fruit may increase the potential for pathogens to survive and/or grow. Fruit pickers and handlers with infections are also an important source of contamination.

Vegetables in oil

This product category includes a diverse range of vegetables and mixtures of vegetables and herbs that may be used fresh, dried, roasted or acidified. Oil is added to exclude air, which prevents discoloration of the vegetable. Although immersion of vegetables in oil reduces the available oxygen in the container, contrary to popular belief, it does not preserve the food. Some pathogenic bacteria are able to survive and grow in reduced levels of oxygen and even under anaerobic conditions.C. botulinum is the main pathogen of concern because of its ability to grow anaerobically and it has been linked to outbreaks of illness from the consumption of vegetables in oil. Vegetables may be contaminated by C. botulinum spores, which are frequently associated with soil, and processes such as cooking and acidification may be insufficient to inactivate the spores or prevent their germination and growth. Acidification to below pH 4.6 should prevent outgrowth; however, more than one hurdle is recommended as a safeguard.

Seed sprouts

Seed sprouts are usually consumed raw and include alfalfa, mung bean, chickpeas, cress, fenugreek, soy, lentils, sunflower, onion, and radish. Seeds for sprouting generally do not receive any special treatment during harvesting and transport, and so may become contaminated with pathogenic organisms in the field or during harvesting, handling, processing, and distribution. While some bean sprouts may be cooked prior to consumption, many others are consumed raw, for instance with salads.

The microbiological pathogens frequently found associated with seeds for sprouting include B. cereus, Salmonella serovars, and E. coli and these organisms have also been implicated in foodborne illness outbreaks. The rough surfaces and cracks in the seed may protect the pathogens from microbiocidal treatments and may make detection during routine analysis difficult. High levels of organic matter also reduce the effectiveness of chlorine treatments during seed washing and seed sprouting. Bacterial populations of 10²–10⁷ cfu/g have been observed on seeds for sprouting, and this natural population can rapidly increase under the high moisture and moderate temperature conditions used in sprouting facilities. Microorganisms may also become internalized in the sprout during growth, so sanitising wash treatments of sprouted seeds are not likely to be effective (FSA, 2000a).

Unpasteurized fruit juice

Fruit juices are made by extracting fruit (citrus juices) or by macerating fruit (grape, cherry, berry, apple juice, etc). This may be followed by clarification, filtration, pasteurisation, and/or other processes to reduce the microbial load. In recent years, there has been a trend to produce ‘natural’ fruit juices containing no preservatives and receiving little or no heat treatment.

Any microorganisms present on the surface of fruit may potentially contaminate the juice made from it. Bacterial pathogens are unlikely to grow due to the low pH but some bacteria, viruses or protozoa may be able to survive for extended periods. The length of time the microorganism may survive is dependent on the pH of the juice, the storage temperature, and the physiological state of the microorganism. Some Salmonella serovars and strains of pathogenic E. coli are known to be particularly acid tolerant, with this response thought to be activated by previous exposure to sub-lethal pH values.

Apple and pear juice can become contaminated by the mycotoxin patulin, which is produced by several Penicillium and Aspergillus species. P. expansum appears to be the main patulin producer in apples and apple products. Since patulin is concentrated in the rotting tissue of fruit, it is a good indicator of the quality of fruit used to make the juice.

The acidic nature of fruit juices makes them corrosive to metals. To avoid potential chemical contamination, only stainless steel or corrosion resistant vessels should be used to store these products. Other metals such as copper can leach into the beverage during storage.

3.2.2. Exposure assessment

Production data

Leafy salad vegetables, such as lettuce, rocket, and baby spinach, are the most common products in the fresh cut category.Based on limited industry information, the estimated annual consumption of fresh cut fruit and vegetables is:11,000 tonnes of fresh cut vegetables, 150 tonnes of fresh cut fruit, approximately 1000 tonnes of vegetables in oil, and between 2100 and 2600 tonnes of seed sprouts. Fruit juice suppliers suggest that manufacture of unpasteurized fruit juices occurs at relatively low volume, about 100,000 L/year, not including juices prepared in retail premises.

Consumption of plant products

Consumption of fruits, during the period 1997–98 and 1998–99, increased by 8.3% from 124.7 kg per capita to 135.0 kg. In the same period, the import of oranges and other citrus fruit rose by more than 62%.Consumption of vegetables has shown a steady 9.4% increase over the last decade. Per capita consumption of tomatoes showed a significant increase from 20.9 kg in 1997–98 to 24.9 kg in 1998–99, a rise of 19%. The category of other vegetables showed a 4.6% increase in consumption in 1998–99 to 25.1 kg per person.Approximately 35% of all respondents consumed fruit juices and drinks, with the mean consumption being 250mL per day.

Prevalence of hazards in plant products

Generally, there have been a small number of surveys of plant products. The analysis of 54 samples of ready-to-eat salads and vegetables showed that only one was positive for L. monocytogenes. Szabo et al. (2000) tested 120 minimally processed, cut and packaged lettuce samples. Three samples (2.5%) were positive for L. monocytogenes, 66 samples (55%) were positive for Aeromonas hydrophila or A. caviae and 71 samples (59%) were positive for Y. enterocolitica.The survey of the microbiological quality of freshly squeezed juices showed that L. monocytogenes was detected in 1/291 samples (0.3%), but the level was sufficient to classify the sample as potentially hazardous. E. coli was detected in 7/291 samples (2.4%). In 2006, it was found that E. coliwas detected in 7 out of 261 samples (2.7%) of sprouted seeds from a retail store, while Listeria and Salmonella were not detected in any samples. A sample was found to be potentially hazardous due to the presence of verotoxigenic E. coli (VTEC) and a further two samples were categorized as unsatisfactory due to elevated levels of E. coli. A more extensive survey of 122 samples in 2008 found that 99.2% of sampleswere microbiologically acceptable, with a single sample categorized as unsatisfactory due to B. cereus at a level of 5500 cfu/g. E. coli was detected in 1/119 samples (0.8%) of fresh cut vegetables, while Salmonella, L. monocytogenes and VTEC were not detected in any samples.

The Food Safety Authority of Ireland (FSAI) surveyed the bacteriological safety of a range of plant products as part of a European Commission coordinated program (FSAI, 2003). Pre-cut fruit and vegetables had samples classed as unacceptable/potentially hazardous due to the presence of Salmonella in 1/529 samples (0.2%) and L. monocytogenes in 1/344 samples (0.3%). Qualitative tests found 21/513 samples (4.1%) positive for L. monocytogenes. No sprouted seeds samples were classed as unacceptable or potentially hazardous. L. monocytogenes was detected in 1/26 samples (3.8%). No problems were detected with unpasteurized fruit and vegetable juices.

A similar European Commission program surveyed pre-packed mixed salads from retail premises in the UK for L. monocytogenes.L. monocytogenes was detected in 4.8% of collected samples. A parallel survey by FSAI included Salmonella testing in the survey design. Quantitative analysis detected two samples with L. monocytogenes at levels exceeding 100 cfu/g. Summarized microbiological results of surveys of prepared salads and fruit examined in the UK showed no isolations of E. coli O157 or Campylobacter. Five out of 3852 samples (0.1%) of bagged salad vegetables were positive for Salmonella but other commodities were negative. L. monocytogenes and E. coli were detected in most commodities surveyed, usually at low incidence.

Studies of bacterial pathogens in plant foods in the US (2006 Annus horribilis) showed a drastic increase in contaminated food: sprouts, Salmonella – 100 cases; lettuce, E. coli O121:H19 – 4 cases and E. coli O157:H7– 162 cases; spinach, E. coli O157:H7 – 202 cases; carrot juice; Cl. botulinum - 6 cases; tomatoes, Salmonella – 400 cases; strawberries, suspected L. monocytogenes; cantaloupes and spinach, suspected Salmonella.

3.2.3. Hazard characterisation

Foodborne illness outbreaks from plant products

An indication of the exposure to hazards in plant products is provided by an examination of the foodborne illness outbreaks between 1995 and 2008 attributed to fresh produce and plant products.

Prior to this period, in 1989,in Australia,there were three separate outbreaks from fruit salad due to Salmonella; while in 1991, a nationwide outbreak of Norovirus was attributed to the consumption of unpasteurized orange juice. In addition, the risk of listeriosis from plant products was highlighted by an outbreak of listeriosis from contaminated fruit salad. In 1998–1999, six deaths of elderly patients occurred and nine others were affected.

In 1996, an outbreak of E. coli O157:H7 infection occurred among schoolchildren in Sakai City, Osaka, Japan. The outbreak was attributed to white radish sprouts served in a centralized luncheon program servicing 56 schools. Over 8000 children developed symptoms and 398 children were hospitalized. Two further incidents of E. coli O157:H7 in neighboring areas were also related to white radish sprouts. All the implicated sprouts were traced back to one farm. This illustrates the size of an outbreak that can result when a hazard becomes a reality in a centrally processed and widely distributed product.

In the USA, from 1993 to 1997, there were identified 190 produce-associated outbreaks, resulting in 16,058 illnesses, 598 hospitalisations and eight deaths. The produce-associated outbreaks were an increasing proportion of all reported foodborne outbreaks with a known food cause, rising from 0.7% in the 1970s to 6% in the 1990s. Salad, lettuce, juice, melon, sprouts, and berries constituted the fresh produce most frequently implicated. In the period from 1990 to 2005, there were reported several cases of contamination of greens-based salads, melon, lettuce, and sprouts with Salmonella. Produce-related outbreaks resulted in an average of 47.8 cases, which is higher than the incidence reported for outbreaks from poultry, beef, and seafood. Four further outbreaks that occurred in 2006 were detected: an outbreak traced to fresh spinach contaminated with E. coli O157; salmonellosis traced to tomatoes; and two outbreaks linked to lettuce contaminated with E. coli O157:H7. By January 2007, 205 cases had been reported with 103 hospitalisations, 31 cases of haemolytic uraemic syndrome (HUS), and three deaths confirmed. Contamination was traced back to one farm. While no definitive determination of how the pathogens contaminated the spinach could be made, the presence of wild pigs near the growing fields and the irrigation wells was determined to be an environmental risk factor. Processing of the spinach included washing, but this did not eliminate the problem and may have facilitated the spread of pathogens from contaminated to uncontaminated spinach. This is an example of a widespread outbreak of severe bacterial illness attributable to hygiene failures in the growing and processing of spinach. In 2008, a large outbreak of Salmonella Saintpaul in the USA and Canada was associated with multiple raw produce items. In August 2008, 1442 people were affected, with at least 286 hospitalisations. Moreover, the outbreak might have contributed to two deaths. The epidemiological data suggested that the major vehicle for the spread of the pathogen was jalapeno peppers. However, serrano peppers were also considered to be a vehicle, and early in the outbreak tomatoes were considered a source. Contamination of produce may have occurred on the farm or during processing or distribution. The outbreak strain of Salmonella has been found in one growing area and an associated packing facility in Mexico. This is the largest culture-confirmed outbreak in the USA in the last decade. As many persons with Salmonella illness do not seek care or have stool specimens tested, many more unreported illnesses may have occurred.

In England and Wales,a review of the outbreaks in the period from 1992 to 2006revealed 82 outbreaks related to prepared salads, with 3434 people affected, 66 hospitalisations, and one death.The foodborne illness examples included seven outbreaks of botulism in products of plant origin. The implicated products were commercial garlic-in-oil, hazelnut yoghurt, restaurant potato dip, restaurant aubergine dip, commercial black bean dip, commercial hummus and commercial refrigerated carrot juice. Temperature abuse was suspected to be a contributing factor in four of the outbreaks. In 2007, 55 cases of Salmonella Senftenberg infection in England and Wales were linked to fresh basil. Scotland, Denmark, the Netherlands and the USA reported 19 further cases with the outbreak strain. Eight samples of fresh packed basil from Israel tested positive with the same strain. Microbiological evidence suggested an association between contamination of fresh basil and the cases of Salmonella Senftenberg infection, leading to withdrawal of basil from all potentially affected batches from the UK market (Pezzoli, 2008).

Estimating the number of illnesses, hospitalizations, and deaths caused by major pathogens is an important step in the prioritization of pathogens for disease control programs. Estimating the proportions of these illnesses that are due to specific food sources (foodborne illness source attribution) is a necessary second step to determine the specific interventions needed to reduce illness and to measure progress toward public health goals resulting from food safety policies and interventions. Estimates of foodborne illness source attribution are used for many purposes, including informing strategic planning, informing risk-based decision-making, estimating benefits of interventions, and evaluating the impact of interventions.

Plant products as high risk

As previously discussed, the plant products scoping study ranked five specific plant product as high risk due to specific pathogens. These are discussed as follows.

Fresh-cut vegetables and fresh cut fruit

Listeria monocytogenes

Survey data show that L. monocytogenes occurs in cut vegetables at low prevalence and usually at low levels. L. monocytogenes can grow in a range of vegetables; however growth is typically slow at refrigeration temperatures but numbers can increase by several logs in some commodities stored at 10–15°C for 7–10 days. The potential for growth in refrigerated short shelf-life products would seem to be low. These products have no final cooking process to eliminate contamination. Where productsare packaged by MAP, the potential longer shelf life increases the potential for pathogen growth.

Pathogenic Escherichia coli

There is a potential for pathogenic E. coli to be present on vegetables via direct or indirect contamination with ruminant faeces or from food handlers that carry the organism in their gut. However, surveys of pre-cut vegetables and salads, other than in Mexico, rarely, if ever, detect pathogenic E. coli.

Dose–response for E. coli

A very important indicator of the occurrence of an infectious outbreak is the dose response of the pathogen. Gilbert et al. (2006) reviewed the dose response estimates for E. coli O157:H7 and the original estimates of the infectious dose were less than a few hundred cells. Later work estimated the probability of infection from exposure to differing numbers of cells.One model predicted a dose of 5.9×10⁵ organisms would result in infection in 50% of consumers, while the probability of illness from 100 organisms was 2.6×10^-4. Another study calculated a median dose (50% of people exposed become symptomatic) of 1.9×10⁵ and a probability of 6×10^-2 of infection when exposed to 100 cells. An analysis of data from the Sakai City elementary school outbreak of E. coli O157:H7 indicates much higher probabilities of infection at lower doses than previous models. Gilbert et al. (2006) also reported the dose–response for E. coli O111 and O55. The dose for infection of 50% of the exposed population was 2.6×10⁶ organisms. The probability of illness when exposed to 100 cells was 3.5×10^-4. Gilbert et al. (2006) state that the organism will grow on leafy vegetables at temperatures above 7°C. However, due to the low infectious dose of the organism in food, growth may not be required to cause illness.

Salmonella

In 2003 the incidence of salmonellae in fruit, vegetables and spices was shown to be below 10%. The numbers of salmonellae on raw vegetables are usually <1 cfu/g, but numbers as high as 240 cfu/g have been found on Dutch endive. Jay et al. (2003) also include information about an outbreak in Germany traced to paprika and paprika powdered potato chips which resulted in an estimated 1000 cases of salmonellosis. The numbers of salmonellae detected in the food were very low, around 2.5 Salmonella cfu/g in the paprika and 0.04–0.45 Salmonella cfu/g of chips.

Clostridium botulinum

The risk of botulism is increased for products packaged using MAP, with the longer shelf life increasing the potential for spore germination and pathogen growth. The contributing factors are the low dose required to cause illness, the severity of the illness, the fact that processing increases the risk and the existence of an epidemiological link. That rating remains appropriate, particularly as longer shelf life vegetable products are becoming more available.

Vegetables in oil

The US Food and Drug Administration (FDA) lists a history of botulism attributed to inadequately acidified foods and notes that products processed by 29 firms were found to be inadequately acidified. The FDA concluded that the evidence demonstrated that certain manufacturers of acidified foods did not realize the importance of adequate pH control. Despite the acidified foods regulation being published in 1979, two serious outbreaks of botulism were reported in the 1980s in Canada and the USA. Chopped garlic in oil was clearly identified as the source of botulism toxin. The concern about vegetables in oil and botulism remains current. The products are popular and home production is common.

According to Food Science Australia (FSA), two false assumptions persist about vegetables in oil:

• That the addition of oil has a preservative effect

Incorrect. The only function of the oil is to prevent oxidation from air in the container which can lead to discolouration of some foods. By excluding air from the surface, this establishes anaerobic conditions which actually favor the growth of some types of bacteria, including C. botulinum.

• That some herbs and spices, and especially garlic, have significant anti-microbial properties

Incorrect. The preservative effect of these materials is slight and inconsistent as outbreaks of botulism in Canada and the USA have demonstrated.

While acidification to a pH less than 4.6 would adequately control the outgrowth of C. botulinum, refrigeration is also used in some cases as an additional hurdle.

Seed sprouts

Outbreak investigations have identified several factors that affect the microbiological safety of sprouted seeds. To date, contaminated seeds have been the likely source of most outbreaks. Seed contamination could have occurred at the farm, seed processor, or sprouting facility. The hydrophobic surface of seeds makes sanitation and removal of contaminating microorganisms difficult. Conditions during sprouting (time, temperature, water activity, pH, and nutrients) are ideal for growth of pathogenic bacteria, leading to an increased risk.

3.2.4 Risk assessment

Fresh-cut vegetables and fresh cut fruit

• Listeria monocytogenes

The FDA/USDA (2003) quantitative risk assessment on L. monocytogenes assigned low relative risk rankings to fruits, vegetables, and deli-type salads. While it appears that the probability of infection is low even for persons vulnerable to listeriosis, the consequences of the illness remain severe. The high risk rating is also applied to modified atmosphere products that are stored for extended periods. The potential for growth in storage increases the ranking for MAP vegetables and salads.

• Pathogenic Escherichia coli

There have been a number of E. coli outbreaks attributed to this group of products around the world. The illness consequences are potentially severe with high rates of hospitalization and long-term effects, such as HUS and kidney problems. Food Science Australia rated the risk as high, while Gilbert et al. (2006) placed pathogenic E. coli in the highest severity category but lowest incidence category for New Zealand foods. It was concluded that it is essential that efforts continue to prevent the likelihood of foodborne transmission from this group of organisms.

• Salmonella serovars

The risk of Salmonella in these high-riskproducts is based on the severity of the illness and no consumer cooking step to eliminate the hazard. Significant risk of Salmonella serovars in fruit and vegetables is based on similar criteria to those defined by FSA, but it should be borne in mind that the increase in their production is not a condition for possible disease. This appears consistent with the many outbreaks attributed to products in which Salmonella might survive but not grow.

• Clostridium botulinum

FSArated the risk of C. botulinum in these products as high. The contributing factors are the severity of the illness, the fact that processing and packaging using MAP may increase the risk and the existence of an epidemiological link. There is no domestic epidemiological evidence to support the high risk ranking but, to date, longer shelf life vegetable products have had limited availability.

• Vegetables in oil

There appears to be clear potential for products prepared without appropriate control measures to result in a poorly acidified product, with potential to cause severe illness from pathogens such as C. botulinum. These products are sometimes prepared by small and medium enterprises, which is considered to increase the risk if knowledge of food safety controls is not adequate.

• Seed sprouts

The conditions during sprouting (time, temperature, water activity, pH, and nutrients) are ideal for growth of pathogenic bacteria such as Salmonella and pathogenic E. coli, leading to seed sprouts being considered a high risk product. The potential for growth of pathogenic organisms during sprouting increases the risk substantially, and there is epidemiological evidence to demonstrate that contamination does occur. The implementation of control measures, such as sanitation of seeds prior to sprouting, may lower the prevalence of pathogens.

• Unpasteurized fruit juice

The high risk ranking of unpasteurized juice is appropriate. The potential sources of contamination are virtually identical as those in fresh cut fruit, and there is strong epidemiological evidence to justify the risk. The two large-scale outbreaks in Australia, in 1991 and 1999, due to contamination of unpasteurized juice with Salmonella serovars have clearly demonstrated the potential for unpasteurized juice to cause illness.