In 2004, OzFoodNet sites recorded 24,313 notifications of eight potentially foodborne diseases, along with 118 outbreaks of foodborne disease. Overall, reports of both notifications and outbreaks were higher than previous years. The most common sporadic diseases were campylobacteriosis (15,640 cases) and salmonellosis (7,842 cases). Reports of sporadic cases of Shiga toxin-producing Escherichia coli were rare with only 46 cases, but there were two small clusters due to serotypes O157/O111 and O86. The 118 foodborne disease outbreaks affected 2,076 persons, of whom 5.6 per cent (116/2,076) were hospitalised and two people died. Foods prepared in restaurants and catering settings caused the most outbreaks and the most common agent was Salmonella Typhimurium. Outbreak investigations during 2004 implicated chicken, foods containing eggs, imported oysters and food handlers infected with norovirus. In addition to foodborne outbreaks, OzFoodNet sites reported 874 outbreaks that were spread from person-to-person affecting 25,363 people. Sites conducted 54 investigations into clusters of Salmonella and other pathogens where a source could not be identified. Surveillance of foodborne diseases continued to improve during 2004, with all jurisdictions contributing to national cluster reports and using analytical studies to investigate outbreaks. Ninety-eight per cent of Salmonella notifications on state and territory surveillance databases recorded complete information about serotype and phage type. Foodborne disease may cost Australia as much as $1.2 billion annually making it vital to intervene to prevent disease. Commun Dis Intell 2005;29:164–191.

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Introduction

Foodborne disease is a major cause of morbidity and an occasional cause of mortality throughout the world.^1,2 Each year there are approximately 5.4 million cases (95% Credible Interval 4–6.9 million cases) of foodborne gastroenteritis in Australia, resulting in 80 deaths annually.³ Approximately 32 per cent (95% Credible Interval 28%–38%) of all gastroenteritis in Australia is estimated to be foodborne.

Many countries conduct surveillance of potentially foodborne diseases to protect consumers and maintain a safe food supply.^4,5 The major aim of surveillance of diseases that arise from contaminated food is to detect outbreaks. Investigation of foodborne outbreaks have many clear public health benefits, as early intervention can remove contaminated product from the marketplace and contribute to policies to prevent further disease.⁶ The public health benefits of surveillance and early outbreak detection have clear economic benefits.⁷

In addition, countries are increasingly using data from surveillance systems to support and monitor interventions in the food supply chain. One example is the use of the United States of America Centers for Disease Control and Prevention's FoodNet data to establish whether national disease targets set under the 'Healthy People 2010' initiative have been met (www.healthypeople.gov). FoodNet has been able to track the incidence of laboratory-diagnosed cases of foodborne disease that are not notifiable to State health departments.⁸ Recent results from FoodNet indicate sustained declines in the incidence of several diseases, including salmonellosis and campylobacteriosis.⁹ This is supported by findings in the United States of America meat industry that have recorded declining isolation of Salmonella and Campylobacter in meat processing plants.¹⁰

In 2000, the Australian Government Department of Health and Ageing ( DoHA ) established the OzFoodNet network to enhance surveillance for foodborne disease.¹¹ This built upon an 18-month trial of active surveillance in the Newcastle region of New South Wales that was modelled on the FoodNet surveillance system. The OzFoodNet network consists of epidemiologists specifically employed by each state and territory health department to conduct investigations and applied research into foodborne disease. The Network involves many different organisations, including the National Centre for Epidemiology and Population Health, and the Public Health Laboratory Network. OzFoodNet is a member of the Communicable Diseases Network Australia, which is Australia's peak body for communicable disease control.¹² The Australian Government Department of Health and Ageing funds OzFoodNet and convenes a committee to manage the Network, and a committee to review the scientific basis for various research projects.

This is the fourth annual report of OzFoodNet and covers data and activities for 2004.

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Methods

Population under surveillance

In 2004, the coverage of OzFoodNet included all states and territories. The entire Australian population was estimated to be 20,111,297 persons in June 2004. 13 In addition, the Hunter Area Health Service had a separate OzFoodNet Site complementing foodborne disease surveillance across New South Wales. The Hunter site conducts thorough local investigation and provides a baseline for foodborne disease incidence in New South Wales. In June 2004, the population covered by the Hunter site was estimated to be 549,846 persons.

Data sources

Rates of notified infections

All Australian states and territories require doctors and/or pathology laboratories to notify patients with infectious diseases that are important to public health. Western Australia is the only jurisdiction where laboratory notification is not mandatory under legislation, although most laboratories still notify the health department by agreement. OzFoodNet aggregated and analysed data on patients notified with the following diseases or conditions, a proportion of which may be acquired from food:

• Campylobacter infections;
• Salmonella infections, including Salmonella Paratyphi A, B and C;
• Listeria infections;
• Yersinia infections;
• Shiga toxin-producing Escherichia coli infections and haemolytic uraemic syndrome;
• typhoid; and
• Shigella infections.

To compare disease to historical totals, OzFoodNet compared crude numbers and rates of notification to the mean of the previous six years. Where relevant, numbers and rates of notifications for specific sub-types of infecting organisms were compared to notifications for the previous year.

To calculate rates of notification the estimated resident populations for each jurisdiction for June 2004, or the specified year, were used.¹³ Age specific rates for notified infections in each jurisdiction were calculated.

The date that notifications were received was used throughout this report to analyse notification data. These data are similar to those reported to the National Notifiable Diseases Surveillance System, but individual totals may vary with time and due to different approaches to analysis.

Gastrointestinal and foodborne disease outbreaks

OzFoodNet collected information on outbreaks of gastrointestinal disease, including foodborne illness, that occurred in Australia during 2004. An outbreak of foodborne disease was defined as an increase in the number of reports of a particular infection or illness associated with a common food or meal. The reports collate summary information about the setting where the outbreak occurred, where food was prepared, the month the outbreak occurred, the aetiological agent, the number of persons affected, the type of investigation conducted, the level of evidence obtained and the food vehicle responsible. To summarise the data, OzFoodNet categorised the outbreaks by aetiological agents, food vehicles and settings where the outbreak occurred. Data on outbreaks transmitted from infected persons, water, animals and cluster investigations were also summarised. The number of outbreaks and documented causes may vary from summaries published by different jurisdictions.

Risk factors for infection

To identify risk factors for foodborne infection in Australia, OzFoodNet reviewed summary data from outbreaks that occurred in 2004 and compared them to previous years. Data from several complementary OzFoodNet studies of foodborne illness in Australia were also examined.

Surveillance evaluation and enhancement

To identify areas where improvements to surveillance are critical, OzFoodNet compared the results of surveillance across different sites, including rates of reporting outbreaks, and investigation of clusters of Salmonella. To measure how well jurisdictions conducted surveillance for Salmonella, OzFoodNet examined the completeness of information contained on state and territory databases in 2004. The proportion of notifications with serotype and phage type information was compared with results for the previous three years.

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Author affiliations

The OzFoodNet Working Group is (in alphabetical order): Rosie Ashbolt (Tas), Jenny Barralet (Qld), Robert Bell (Qld), Andrew Black (ACT), Barry Combs (SA), Christine Carson (WA), Craig Dalton (Hunter PHU), Karen Dempsey (NT), Gerard Fitzsimmons (DoHA), Joy Gregory (Vic), Gillian Hall (NCEPH), Bridget Hardy (DAFF), Michelle Harlock (NT), Geoff Hogg (MDU), Melissa Irwin (NSW), Geetha Isaac-Toua (ACT), Martyn Kirk (DoHA), Karin Lalor (Vic), Deon Mahoney (FSANZ), Tony Merritt (Hunter PHU), Rosanne Muller (NT), Sally Munnoch (Hunter), Jennie Musto (NSW), Lillian Mwanri (SA), Chris Oxenford (DoHA, NCEPH), Rhonda Owen (DoHA), Jane Raupach (SA), Mohinder Sarna (WA), Cameron Sault (Tas), Russell Stafford (Qld), Barbara Telfer (NSW), Marshall Tuck (NSW), Leanne Unicomb (Hunter PHU), Hassan Vally (WA), Kefle Yohannes (DoHA)

Corresponding author: Mr Martyn Kirk, Coordinating Epidemiologist, OzFoodNet, Australian Government Department of Health and Ageing, GPO Box 9848, MDP 15, Canberra, ACT 2601. Telephone: +61 2 6289 9010. Facsimile: +61 2 6289 5100. Email: martyn.kirk@health.gov.au

 

This article was published in Communicable Diseases Intelligence Vol 29 No 2, June 2005.