Foodborne Illness in Australia: Annual Incidence Circa 2010

Foodborne illness in Australia: Annual incidence circa 2010

Foodborne illness in Australia: Annual incidence circa 2010

Authors: Martyn Kirk, Kathryn Glass, Laura Ford, Kathryn Brown and Gillian Hall, National Centre for Epidemiology and Population Health, Australian National University.

Prepared for the Australian Government Department of Health, New South Wales Food Authority and Food Standards Australia New Zealand by the National Centre for Epidemiology and Population Health, Australian National University.

Online ISBN: 978-1-74186-170-9

Publications approval number: 10768

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Glossary and Acronyms

Foodborne illness in Australia circa 2010

Asymptomatic

GBS

CrI

DALY

Delphi process

Foodborne illness

HUS

IBS

ICD-10-AM

IID2

Incidence

Monte Carlo simulation

Notifiable

NGSI

NGSII

A state where a person who is infected does not show any symptoms.

Guillain-Barré syndrome – a disorder where the body’s immune system attacks the peripheral nervous system and may be the result of a preceding infectious event.

Confidence interval –represents a range of values that act as good estimates for an unknown parameter usinga frequentist distribution.

Credible interval – represents a range of values where the most likely estimate might lie using a posterior probability distribution.It may be interpreted similar to confidence intervals.

Disability adjusted life year – a metric to describe the burden of disease that takes into account the morbidity and mortality of a condition.

A method for structuring a group communication process so that the process is effective in allowing a group of individuals, as a whole, to deal with a complex problem.

Any illness resulting from the consumption of contaminated food, pathogenic bacteria, viruses or parasites that contaminate food.

Haemolyticuraemic syndrome – a disorder where blood cells are destroyed injuring the kidneys; often occurring following infection with toxin-producing bacteria.

Irritable bowel syndrome – chronic abdominal pain, bloating, constipation and diarrhoea; often triggered as the result of bacterial gastroenteritis.

International Statistical Classification of Diseases and Related Health Problems, Tenth Revision, Australian Modification.

The second longitudinal study of infectious intestinal disease in the United Kingdom by Tam et al.1

The rates at which new cases occur in a population in a specific time period.

A computerised mathematical technique that performs risk analysis by building models of possible results by substituting a probability distribution for any factor that has inherent uncertainty and producing distributions of possible outcome values.

An infection that doctors, laboratories, or other health professionals must report or notify to health departments for the purpose of prevention and control.

National Gastroenteritis Survey I – a nationally representative cross-sectional survey conducted in Australia in 2001–2002.

National Gastroenteritis Survey II – a nationally representative cross-sectional survey conducted in Australia in 2008–2009.

NNDSS

OzFoodNet

OzFoodNet outbreakregister

Prevalence

ReA

STEC

WQS

National Notifiable Diseases Surveillance System – the national system of surveillance for infectious diseases in Australia.

An Australian network for enhanced surveillance of foodborne disease established by the Australian Government Department of Health in 2000 with Australia’s state and territory health authorities. OzFoodNet investigates multi-jurisdictional outbreaks of disease, provides understanding of the causes and incidence of foodborne disease in the community, and provides evidence for policy formulation.

A register of data on outbreaks of gastrointestinal and foodborne diseases that was established in 2000.

The proportion of the population that has a condition at a given point in time, including new and chronic cases of disease.

Reactive arthritis – arthritis following bacterial infection; previously known as Reiter’s syndrome.

Shiga toxin-producing Escherichia coli – strains of E. coli producing Shiga toxins, which may result in haemolytic uraemic syndrome.

Water Quality Study – A randomised controlled trial conducted in Melbourne in 1997–1999 to examine whether reticulated water meeting national guidelines resulted in gastroenteritis by Hellard et al.2

Foodborne illness in Australia circa 2010

Executive Summary

Foodborne illness causes significant morbidity and occasional mortality in Australia. Reports of disease outbreaks linked to contaminated food are common and may result in damage to specific food businesses, related food businesses and whole industries. Lost productivity, impacts on lifestyle and medical expenses from foodborne illness can result in a substantial burden for Australia. The costs of foodborne illness highlight the need to improve efforts to prevent disease and strengthen food safety.

Understanding the epidemiology of diseases that occur as a result of contaminated food is complicated, as there are many different agents that can cause illness. While the majority of foodborne pathogens cause gastroenteritis, there are some that result in different illnesses, such as meningitis and hepatitis. Only a fraction of cases of foodborne illness are reported to health departments and investigated, and for many diseases it is not mandatory for doctors and laboratories to report cases to health departments for investigation. It is necessary to use novel methods and analyse multiple datasets to estimate incidence and outcome of foodborne illness, including notifiable disease reports, laboratory data, outbreak surveillance reports, expert opinion and the literature.

This report estimates the number of cases of illness and common sequelae acquired in Australia from contaminated food, circa 2010. It also estimates the number of hospitalisations and deaths due to foodborne illnesses and sequelae. Uncertainty in the data is accounted for by reporting 90% Credibleintervals (CrI) and comparing estimates using different sources of data and over time.

Circa 2010, there were an estimated annual 4.1 million (90% CrI: 2.3–6.4 million) cases of foodborne gastroenteritis acquired in Australia, along with 5,140 (90% CrI: 3,530–7,980) cases of non-gastrointestinal illness and 35,840 (90% CrI: 25,000–54,000) cases of sequelae. Norovirus, pathogenic Escherichia coli, Campylobacterspp. and non-typhoidalSalmonella spp. were the most common known causes of foodborne gastroenteritis, although approximately 80% of illnesses are of unknown pathogens. Approximately 25% (90% CrI: 13%–42%) of the 15.9 million episodes of gastroenteritis that occur in Australia were estimated to be transmitted by contaminated food. This equates to an average of approximately one episode of foodborne gastroenteritis every five years per person. Data on the number of hospitalisations and deaths represent the occurrence of serious foodborne illness. Including gastroenteritis, non-gastroenteritis and sequelae, there were an estimated annual31,920 (90% CrI: 29,500–35,500) hospitalisations due to foodborne illness and 86 (90% CrI: 70–105) deaths due to foodborne illness circa 2010.

A main aim of this study was to compareif foodborne illness incidence had increased over time. In this study, similar methods of assessmentwere applied to data from circa 2000, which showed that the rate of foodborne gastroenteritis had not changed significantly over time. Two key estimates were the total number of gastroenteritis episodes each year, and the proportion considered foodborne. In circa 2010, it was estimated that 25% of all episodes of gastroenteritis were foodborne. By applying this proportion of episodes due to food to the incidence of gastroenteritis circa 2000, there were an estimated 4.3 million (90% CrI: 2.2–7.3 million) episodes of foodborne gastroenteritis circa 2000, although credible intervals overlap with 2010. Taking into account changes in population size, applying these equivalent methods suggests a 17% decrease in the rate of foodborne gastroenteritis between 2000 and 2010, with considerable overlap of the 90% credible intervals.

For certainspecific foodborne illnesses datawere compared from 2000 and 2010 to examine whether they are increasing or decreasing. For example, foodborne salmonellosis was estimated to have increased from 28,000 annual infections circa 2000 to 39,600annual infections circa 2010; a rate increase of 24% from 1,500 cases per million to 1,850 cases per million annually. Similarly, for foodborne campylobacteriosis there were 139,000 infections circa 2000, rising to 179,000 infections circa 2010; representing a 13% increase in incidence from 7,400 cases per million to 8,400 cases per million annually. Illnesses from hepatitis A decreased from 245 cases circa 2000 to 40 cases circa 2010, representing a rate decrease of 85% from 13 cases per million to two cases per million annually.

The findings of this study are similar to recent estimates in the United States of America (USA), Canada and other countries. These estimates take into account improvements in understanding foodborne illnesses and the agents responsible, improved information sources, and advances made in methodological approaches. Where possible, contemporary Australian data collected at or around 2010were used.

The results of this study will improve the understanding of the epidemiology of specific pathogens and foodborne causes of gastroenteritis in Australia. This will assist in prioritizing foodborne illness for intervention. It is important that Australian governments and industry work together to reduce the incidence of preventable foodborne illness and educate consumers about good hygiene and food safety strategies.

Acknowledgements

The Australian Government Department of Health, New South Wales Food Authority and Food Standards Australia New Zealand would like to thank the many people who helped with the conduct of this study and the production of this report. This report was authored by Dr Martyn Kirk, Dr Kathryn Glass, Ms Laura Ford, Dr Kathryn Brown and Dr Gillian Hall of the National Centre for Epidemiology and Population Health, under contract to the commissioning agencies. The Communicable Diseases Network Australia provided data from the National Notifiable Diseases Surveillance System on notifications of infectious causes of gastroenteritis. State and territory health departments, public health laboratories and OzFoodNet epidemiologists also provided data used in this study. The commissioning agencies and the authors thank Drs Martha Sinclair and Karin Leder for providing Water Quality Study data for this study. This work was funded by the Australian Government Department of Health, New South Wales Food Authority and Food Standards Australia New Zealand.

Foodborne illness in Australia circa 2010

Introduction

In 2000, it was estimated that every Australian would experience an episode of gastroenteritis due to food every four years.3The economic costs of foodborne illness are substantial from medical practitioner visits, antibiotic prescriptions and days of work lost each year. The total cost of foodborne illness in Australia is largelyattributable to productivity and lifestyle costs, premature mortality and health care services.4This,largely preventable, burden of foodborne illness to the Australian community highlights the need to continue to improve food safety in Australia.

This report presents an updated estimate of the incidence of foodborne illness in Australia, circa 2010. It is important to regularly update estimates for foodborne illnesses, due to improvements in methods of estimation and changing incidence of disease. There are many different influences on the incidence of foodborne illness, including:

new regulatory measures aimed at preventing infections;
changing agricultural and manufacturing practices;
trends in the way food is prepared, along with consumers’ food choices and changes in eating patterns;

international distribution of food;

emergence of new pathogens; and
identification of new and emerging strains of common infectious agents, such as those that are resistant to antibiotics.

In order to ensure that the estimate of the incidence of foodborne illness in Australia is internationally comparable, the approach first used by Mead et al.5and subsequently by Scallan et al.6in the USA has been adopted. This approach entails determining the total amount of gastroenteritis in the country and secondly the proportion of gastroenteritis that is foodborne. The product of these two estimates gives the total number of cases of foodborne gastroenteritis. However, a slightly different list of pathogens to those used in the study by Scallan et al.6has been selected, including pathogens and illnesses of particular relevance to Australia. Additionally, this report estimates the incidence of sequelae occurring as a delayed reaction to episodes of acute gastroenteritis, such as Reactive arthritis (ReA), irritable bowel syndrome (IBS), haemolyticuraemic syndrome (HUS) and Guillain-Barrésyndrome (GBS).

There are many challenges associated with quantifying the true incidence of foodborne illness in the community. A wide variety of different pathogens produce symptoms of gastroenteritis. Often clinical cases of gastroenteritis are assessed as ‘presumed infectious’ and a pathogen is never identified, either because a stool test is not performed, the stool test fails to identify a known pathogen, or because the pathogen is totally unknown. Scallan et al.7estimated that in the USA, 38.4 million (90% CrI: 19.8–61.3 million) episodes, or 80% of domestically acquired foodborne illness were caused by unspecified agents. Only a few decades ago, pathogens such as Campylobacter spp., Shiga toxin-producing Escherichia coli(STEC), and norovirus were completely unknown.3

One of the most uncertain areas is estimating what proportion of illnesses is due to contaminated food. Most of the pathogens included in this study may be transmitted to humans through contaminated foods or water, as well as from other infected persons, from the environment or from animals. To account for this, expert elicitation was used to estimate the proportion of illness thought to result from contaminated food.

Most cases of gastroenteritis are mild and self-limiting and most people do not visit a doctor or submit a specimen for testing. In Australia, state and territory health departments forward reports of gastrointestinal diseases such as campylobacteriosis, cryptosporidiosis, salmonellosis, STEC and shigellosis to the National Notifiable Diseases Surveillance System (NNDSS). However, if people suffering gastroenteritis do not visit a doctor or submit a specimen for testing their illness will not be recorded in either NNDSS or in state surveillance systems.

Not all foodborne illnesses are notifiable to health departments, for example campylobacteriosis is not notifiable in New South Wales (NSW), norovirus, which is one of the most common causes of gastroenteritis in the developed world, is not notifiable to the NNDSS and poisoning by ciguatera is only recorded in Queensland. Surveillance data represents only a small fraction of the total incidence and multipliers are devised to adjust for underreporting and incomplete population coverage in the Australian surveillance system as well as for infections acquired overseas. The uncertainty in estimates must be taken into consideration. The approach used in the current study was to quantify each component of uncertainty with a plausible probability distribution. Simulations of these distributions were then used to generate an interval that contains the credible estimates of the number of foodborne cases of gastroenteritis.

In this report, improvements in the understanding of foodborne illness and the agents responsible since circa 2000 are taken into account. Specifically, these estimates circa 2010 are based upon new data from:

a review of the literature to determine the best methodological approaches to estimating foodborne illness;
a nationally representative gastroenteritis survey conducted in 2008–9;
updated estimates of underdiagnosis and underreporting of infectious foodborne illnesses to surveillance;
an expert consultation to determine which pathogens and potentially foodborne toxins are currently considered to be of most concern;
an expert elicitation to estimate the proportion of several key pathogens that are transmitted by contaminated food;
NNDSS, state surveillance and the OzFoodNet outbreak register;
hospitalisation separations from each state and territory in Australia; and
mortality statistics for all of Australia from the Australian Bureau of Statistics (ABS).

Although there are many challenges in estimating foodborne illness, the estimates are valuable for development of public health policy. These estimates provide big-picture information on the safety of food in Australia and help to evaluate national intervention and control strategies. In addition, the updated foodborne illness estimates provide a rational basis for undertaking additional costing studies. This report provides an updated picture on the incidence of foodborne illness in Australia circa 2010.

Aims

The aims of this study were to:

estimate the incidence, hospitalisations and deaths due to domestically acquired foodborne illness in Australia circa 2010, and
examine whether there have been changes to the incidence of foodborne illness over time.

Comparing Foodborne illness Internationally

Estimation of the incidence of foodborne illness has proven important for public health policy, both in Australia and internationally.3,8,9 Studies to estimate incidence require complex methods due to the need to synthesize information from various sources, on many different pathogens and agents, and the need to consider many outcomes of illness. The literature was examined to review national studies in other countries that estimated the incidence of foodborne illness due to different pathogens. This included the previous Australian study estimating foodborne illnessincidence circa 2000.10The report reviews methods used to estimate the incidence of foodborne illnesses from nine key papers, which were the:

USA assessment of 28 different pathogens or agents in 19995
USA assessment of 30 different pathogens or agents in 20116,7
France assessment of 24 pathogens or agents published in 200511
Australia circa 2000 assessment of 25 pathogens, agents or sequelae, published in 20053,10
United Kingdom (UK) assessment of 24 pathogens or agents, published in 200212
Greece assessment of 15 pathogens or agents, published in 201113
Netherlands assessment of 18 pathogens, agents or sequelae, published in 201214
New Zealand assessment of 10 pathogens or agents, published in 200015
Jordan assessment offour pathogens or agents, published in 2009.16

Recent national burden of foodborne illness estimates are shown in Table 1 for Greece,13UK,12 France,11 Australia,3 New Zealand,15 USA,6,7 Canada,17 and the Netherlands.14Itshould be noted when directly compare these figures that the definition of ‘foodborne illness’ varies considerably across studies. Excluding the Australian figures, the incidence rates per million inhabitants per year ranged widely across countries from 4,500 cases in France to 369,305 cases in Greece. Hospitalisation rates per million inhabitants per year ranged from 173 in France to 905 in Greece, and deaths per million inhabitants per year ranged from three in Greece to 12 in France. When the incidence rates are compared across all countries with estimates, Greece has the highest incidence, followed by Australia, USA, New Zealand, the Netherlands, UK, and lastly France. In these studies, a similar pattern was seen for the rate of hospitalisations across countries, and deaths ranged from two to 12 foodborne deaths per million inhabitants (Table 1).