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International spread of foodborne illness

The chocolate and halva incidents reported in this issue highlight the way in which foodborne illness and the organisms causing the illness can cross national boundaries.

This has important implications for national authorities and it also means that public health officials and the food industry must be constantly aware of the association of certain products with pathogenic microorganisms even if there is no history of related foodborne incidents in their own country.

Seed sprouts and pathogens

We have discussed at length (Food Safety & Hygiene, November 2000) the association between seed sprouts and a range of pathogens causing foodborne illness including Salmonella spp. and enterohaemorrhagic Escherichia coli.

To date, there is no recorded outbreak in Australia attributable to sprouts. However seed is the usual source of contamination, and seed from Australia has been implicated in outbreaks overseas. (Food Safety & Hygiene, November 2000). Mung beans and alfalfa seeds were the products involved in these incidents.

From the United States a new report (CDC Morbidity and Mortality Report 51. 01 2002 7-9) has identified cases of illness in four States caused by the rarely reported Salmonella kottbus early in 2001. A significant association was found between eating alfalfa sprouts and illness in 32 affected individuals. An investigation by authorities revealed a single producer as the source of the contaminated sprouts.

A review of the sprouter's production records indicated that a single seed lot was associated with the dates of the onset of illness. A culture of samples from this seed lot revealed the presence of S. kottbus. Cultures from two floor drains in the production facility also yielded S. kottbus and the isolates from patients, seed and the facility provided the same molecular typing patterns.

The seed had been imported from Australia in November 2000.

At the farm level, seeds which may end up as seeds for sprouting are treated in the same way as any other agricultural commodity. They may become contaminated through the use of untreated water, improperly composted manure as fertiliser, excretion or run off from animal production or improperly cleaned harvesting or other equipment.

The seeds are notoriously difficult to decontaminate (International Journal of Food Microbiology 52 1999 123-153) but it is essential that a decontamination treatment is used and monitored.

In this case, at least some of the seeds involved underwent a heat treatment followed by a 2,000 mg/L sodium hypochlorite soak for 15 minutes. The U.S. Food and Drug Administration (FDA) recommends a 20,000 mg/L sodium hypochlorite soak for 15 minutes. While the use of this severe treatment might reduce the risk of sprout-related illness, it does not appear to be completely effective. In addition, such a severe treatment can impair germination and the search continues for alternative methods to reduce the risk associated with consumption of raw sprouts.

The FDA recommends that 'persons at high risk of bacterial infection' should not eat raw sprouts. Persons at high risk include the aged, the young, the immunocompromised and pregnant women.

Blueberries and hepatitis

In a completely separate incident, blueberries from a specific distributor in New Zealand are the subject of a health warning from that country's public health authorities. An investigation into an unusually high number of hepatitis A cases in Auckland found 17 of 29 cases since January of this year were linked to blueberries (http://www.promedmail.org and access Archive Number 20020416.3969 published 16 April 2002).

Investigation revealed that a person carrying the highly infectious virus was at the blueberry producer's premises during part of the harvesting period. At least some of the berries linked with the Auckland cases were from this farm.

The New Zealand authorities are warning that the implicated fruit should be discarded even if frozen. The hepatitis A virus is not destroyed by freezing. We noted in Food Safety & Hygiene February 2002, that viral infections, including hepatitis A, have been associated with berry fruits overseas. Hepatitis A represents a particular problem in this regard because viral shedding may begin several days before the onset of symptoms and continue for some time after systems have ceased.

Again there is no record in Australian data of such an association but these fruits must be handled according to best hygienic practice if outbreaks of this type are to be minimised.

The international market-place

The findings from each of the above incidents serve to remind Australian growers and exporters of fresh produce of the need for constant vigilance in monitoring the safety of their product and the product's end-use in international markets.

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Prepared by Keith Richardson and Rachel Jackson
Food Science Australia
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