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Foodborne viral illness in Australia

Little is known of the incidence of foodborne viral illness in Australia. Government sources estimate that 30-40 per cent of the total number of foodborne illness cases are attributable to viruses. This is not dissimilar to estimates made in like countries such as the USA (Emerging Infectious Diseases 5 1999 607 - fulltext here -).

Viral gastroenteritis is usually a relatively mild disease and most people do not consult a doctor. The majority of cases are not reported and not investigated.

However in a current review, Fleet and co-workers at the University of New South Wales (International Journal of Food Microbiology 59 2000 127) point out that in recent years, Norwalk-like virus (NLV) contamination of oysters and orange juice and hepatitis A virus contamination of oysters have been responsible for large outbreaks of foodborne viral disease in Australia.

They also draw attention to the fact that gastroenteritis caused by rotavirus is annually responsible for the hospitalisation of about 12,000 children under the age of five years. Outbreaks of this disease are primarily associated with child care centres, pre-schools and other situations where there are large numbers of children. Outbreaks in adults, especially in nursing homes, can also occur.

Person to person contact is considered to be the principal mode of spread of the virus in these situations but the initial involvement of faecally contaminated foods or water is often suspected. In an earlier review (Medical Journal of Australia 165 1996 672) different authors refer to one outbreak involving 55 individuals where salad vegetables were considered to be the vehicle of infection.

Norwalk-like viruses (NLV)

These viruses first came to the attention of public health officials in Australia in 1977 when oysters harvested from Georges River south of Sydney caused outbreaks of gastroenteritis in the United Kingdom.

The largest outbreak of NLV associated gastroenteritis involved over 3,000 individuals who had consumed orange juice served to passengers on domestic airline flights in 1991. Although the virus was not detected in the orange juice, the outbreak terminated when the juice was withdrawn from sale. Inspection of the production facilities identified several areas where contamination of the juice could have occurred and confirmed the absence of any terminal process lethal to the virus.

Hepatitis A virus

The first documented outbreak of foodborne hepatitis A virus in Australia was attributed to consumption of improperly cooked mussels harvested from faecally contaminated waters in Victoria. However the largest outbreak of the virus occurred in 1996-97 after consumption of oysters harvested from Wallis Lakes in New South Wales (see Food Safety & Hygiene August 2000). Almost 500 people were affected and one person died. A subsequent coronial inquiry revealed numerous sources by which untreated sewage could contaminate the lake and oyster cultivation areas.

More stringent quality assurance programs for oyster cultivation and processing have been implemented to decrease the risk of similar occurrences in the future. Sporadic outbreaks of foodborne hepatitis A virus occur throughout the country. According to the reviewers, they usually involve foods at restaurants. One such case involving a Sydney restaurant and consumption of imported prawns was the subject of subsequent court proceedings. In this case, the judge ruled that even if the prawns were contaminated when purchased by the restaurant, the restaurant owners were culpable for not ensuring that cooking of the prawns was sufficient to kill any contaminating virus.

The review also discusses astroviruses, adenovirus and other viruses and the possible role of foodborne transmission. The authors concluded that management of foodborne viral disease largely depends upon the proper implementation of HACCP principles and that these should be adapted to account for specific viral hazards.

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Prepared by Keith Richardson and Rachel Jackson
Food Science Australia
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