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Food Focus August 2008

Pathogens in fruits and vegetables

Fruit and vegetables are an important part of a balanced diet. Internationally, however, there have been outbreaks of foodborne illness directly attributed to produce, and NZFSA commissioned a review to assess the risks in New Zealand

In recent years a number of overseas outbreaks of foodborne illness have been attributed to fresh produce grown in areas with poor water and fertiliser quality, and/or a lack of effective decontamination measures. Given events overseas, NZFSA felt it was time to take a closer look here.

Pathogen contamination can occur at a number of points during production, harvest, processing, distribution and sale of fresh produce.

Internationally, outbreaks have been caused by contaminated irrigation water, poor hygiene practices and improperly treated manures. Fruit and vegetables can also pick up viruses and other bacterial pathogens, such as Shigella, through cross-contamination and/or poor food handling practices. These are all recognised as possible risk pathways in New Zealand.

The problem pathogens

Salmonella and E. coli O157:H7, and to a lesser extent protozoa and viruses, have most often been found in overseas fresh produce outbreaks. E. coli O157:H7-related illness is not common in New Zealand. It has so far not been found in the few surveys carried out on both conventional and organic produce and hence is not such a concern in domestic produce here.

At-risk produce

Particular produce items have dominated the international food safety literature. Green leafy vegetables, such as spinach and lettuce, have been especially prominent, mainly due to the ease with which they can become contaminated in the growing environment. They can also trap pathogens in the leaves.

Melons, tomatoes and raw berries have been linked to contamination with bacteria, protozoa and viruses, either via production or harvesting.

Unpasteurised fruit juices, previously considered safe due to their acidic nature, have caused outbreaks in Australia and elsewhere overseas. Problems with fresh juice tend to stem from use of fruit that has dropped on to contaminated ground before harvesting – a practice that is not recommended.

The sprouting of contaminated seeds can help spread pathogens throughout a production facility via the growing water.

What’s happening in New Zealand?

The Science Group at NZFSA commissioned Environmental Science & Research to review available information about ready-to-eat (RTE) whole and fresh-cut vegetables and fruits, fresh (unpasteurised) juices and sprouts in New Zealand. The purpose was to see if there were any risks with these products. This information will guide NZFSA’s risk-management decisions about the production, sale and consumption of safe produce in New Zealand.

The review included conventional, organic and hydroponically grown vegetables and fresh herbs, nuts and other salad ‘additives’. It didn’t address commodities such as grasses, dried herbs and spices, or those requiring cooking prior to consumption (eg potatoes, pumpkins and other similar vegetables).

Despite the potential for produce-related food safety issues, only one confirmed outbreak – Hepatitis A in raw blueberries – has been documented in New Zealand. However, an outbreak of Salmonella Saintpaul has tentatively been linked to the use of contaminated wash water, and a separate investigation revealed the presence of E. coli O157:H7 in stream water being used as a source of farm-level wash water.

These examples suggest failures in good agricultural practice, either as a consequence of poor hygiene or the possible use of contaminated water. Irrigation and processing water appear to be areas where additional risk management measures may be useful.

In general, New Zealand growers and processors are applying good standards and we haven’t been exposed to the outbreaks that have occurred overseas. Good agricultural practice and food safety programmes have been put in place for production and processing of ready-to-eat produce by the larger produce companies.

Washing with chlorinated water is the main decontamination method in New Zealand, mainly for reasons of practicality and cost. However, the limited effectiveness and potential safety issues associated with the use of chlorine may see producers adopting alternatives such as ozone and iodine.

The review did identify some potential problems, so the Science Group at NZFSA has contracted a nationwide microbiological survey of fresh imported and domestic (conventional and organic) produce to gather more data. It will continue to monitor this sector to identify if risk assessments are needed in specific areas. In addition, the Science Group is examining the use, by all parts of the food industry, of water supplies not registered under the Health (Drinking Water) Amendment Act 2007.