Factors contributing to food safety concerns
Although it is difficult to determine the global incidence of food-borne disease, the World Health Organization (WHO) estimates that in 2005 alone, 1.8 million people died from diarrheal diseases, and in industrialized countries around 30% of the population is estimated to suffer from food-borne diseases each year (WHO, 2007). In the USA, for example, an estimated 76 million cases of food-borne diseases, resulting in 325 000 hospitalizations and 5000 deaths occur each year (Mead et al., 1999).
The increasing incidence of food-borne diseases is due to a number of factors, including changes in food production on the farm, new systems of food process-ing, longer distribution chains, and new food prepa-ration and storage methods. Changing lifestyles have led to a far greater reliance on convenience foods that are prepared outside the home, and which may have a longer preparation to consumption time. In addi-tion, the food chain has become longer and more complex, giving increased opportunities for food contamination. International trade in foods has expanded dramatically, and today the Food and Agriculture Organization of the United Nations (FAO) estimates over 500 million tonnes of food, valued around US$400–500 billion, move in interna-tional trade annually. Globalization of the food trade presents a major challenge to food safety control authorities, in that food can become contaminated in one country and cause outbreaks of food-borne illness in another. It is not unusual for an average meal to contain ingredients from many countries that have been produced and processed under different standards of food safety.
Food-borne diseases are classified as either infections or intoxications. Food-borne infections are caused when viable microorganisms are ingested and these can then multiply in the human body. Intoxications are caused when microbial or naturally occurring toxins are consumed in contaminated foods. Illnesses that relate to the consumption of foods that are contaminated with chemical toxins or microorganisms are collectively referred to as food poisoning.
The health consequences of food-borne illness are varied and depend on such factors as the individual’s susceptibility, the virulence of the pathogen, and the type of disease. Symptoms are often mild and self-limiting in healthy individuals and people recover within a few days from acute health effects. Acute symptoms include diarrhea, stomach pain and cramps, vomiting, fever, and jaundice. However, in some cases microorganisms or their products are directly or indirectly associated with long-term health effects such as reactive arthritis and rheuma-toid syndromes, endocarditis, Reiter syndrome, Guillain–Barré syndrome, renal disease, cardiac and neurological disorders, and nutritional and other malabsorptive disorders. It is generally accepted that chronic, secondary after-effect illnesses may occur in 2–3% of cases of food-borne infections and that the long-term consequences to human health may be greater than the acute disease. In one salmonellosis outbreak, associated with drinking contaminated milk, about 2% of patients developed reactive arthri-tis. It is estimated that up to 10% of patients with hemorrhagic colitis develop hemolytic uremic syn- drome (HUS), a life-threatening complication of Escherichia coli O157:H7 infection characterized by acute renal failure, hemolytic anemia, and thrombocytopenia.
Vulnerable groups tend to be more susceptible to food-borne infections and generally suffer more severe illness because their immune systems are in some way impaired. The immune system of infants and young children is immature. In pregnant women, increased levels of progesterone lead to the downreg-ulation of cell-mediated immunity, increasing the susceptibility of both mother and fetus to infection by intracellular pathogens (Smith, 1999). In older people, a general decline in the body’s immune response occurs with age, as does a decrease in stomach acid production. Immune responses in older people are also adversely affected if that person is malnourished through poor diet. Furthermore, age-related loss of sensory abilities, such as sight and taste, can lead to difficulties in choosing and preparing food. An aging population is one factor influencing the increase in the prevalence of food-borne disease. In 1999, 20% of Europe’s population was older than 60 years of age, but this is predicted to rise to 35% by 2050 (Kaferstein, 2003). Other groups in which the immune system may be suppressed, making them more susceptible to food-borne infection, include cancer patients, transplant patients receiving immu-nosuppressant drugs, and patients with acquired immunodeficiency syndrome (AIDS). In nonindus-trialized countries, political unrest, war, and famine lead to increased malnutrition and can expose poorer populations to increased risk of food-borne disease.
Improved surveillance systems lead to an increase in the reported incidence of food-borne disease. Using information technology, many countries have devel-oped enhanced surveillance systems to gain a better picture of the true incidence of food-borne disease. International outbreaks are more readily detectable with the use of electronic databases for sharing molec-ular typing data (such as PulseNet in the USA and EnterNet in Europe) and rapid alert systems, websites, or list servers. However, even with this enhanced sur-veillance, it is unlikely that statistics reflect the true incidence of food-borne disease worldwide.
As well as morbidity and mortality associated with food-borne diseases, there are direct economic costs incurred, including the cost of medical treatment and industry losses. WHO estimates that in the USA diseases caused by the major food-borne pathogens have an annual cost of up to US$35 billion. The annual cost for illness due to E. coli O157 infections in the USA has been estimated at US$405 million, which includes costs for medical care (US$30 million), lost productivity (US$5 million) and premature deaths (US$370 million); however, this estimate does not include costs due to pain and suffering, and expenditure on outbreak investigations (Frenzen et al., 2005). The cost of salmonellosis in England and Wales in 1992 was estimated at between US$560 million and US$800 million. Over 70% of costs were directly associated with treatment and investigation of cases, and costs to the economy of sickness related to absence from work. In 2006, Cadbury Schweppes, the world’s largest confectionary company, were forced to recall seven Cadbury-branded products in the UK and two in Ireland due to Salmonella con-tamination. The estimated cost of the product recall was £30 million, including a £5 million marketing campaign to rebuild consumer confidence. In addi-tion, Cadbury Ltd in the UK was fined £1 million and ordered to pay costs totaling £152 000 for distributing the contaminated chocolate products which led to illness in 42 people being reported, three of whom were hospitalized (Cadbury press release, 2007).
Bearing these figures in mind, the true estimates of food-borne disease and the likely economic costs are unknown. In industrialized countries only a small proportion of cases of food-borne diseases is reported, and even fewer are investigated. Very few non-industrialized countries have established food-borne disease reporting systems, and in those that have, only a small fraction of cases is reported.
The emergence of new food-borne pathogens is one factor leading to increased concern about food safety. During the twentieth century improvements in sewage treatment, milk pasteurization, and water treatments, and better controls on animal disease have led to the control of food-borne and water-borne diseases such as typhoid, tuberculosis, and brucellosis. However, new food-borne pathogens have emerged. Food-borne organisms such as E. coli O157, Campylobacter jejuni, and Salmonella Enteritidis phage type 4 were virtually unknown in the 1970s, but have come to prominence as virulent pathogens associated with foods of animal origin. Cyclospora cayetanensis emerged as a food-borne pathogen in 1995, when it was associated with outbreaks of illness traced to raspberries imported into the USA from Guatemala.
Cryptosporidium parvum emerged as a pathogen of worldwide significance during the 1990s and has been linked to contaminated drinking water and to a range of foods including salads, unpasteurized milk, and apple juice. Some known pathogens such as Listeria. monocytogenes have only recently been shown to be predominantly food-borne and, since they can grow at refrigeration temperatures, have increased in importance with the expansion of the cold chain for food distribution. Enterobacter sakazakii has recently been implicated in outbreaks of infection associated with powdered infant formula. Many of these emerg-ing pathogens are of animal origin and do not usually cause serious illness in the animal host.
Another concern is that a proportion of food-borne illness is caused by pathogens that have not yet been identified, and therefore cannot be diagnosed. In the USA, it is estimated that unknown food-borne agents caused 65% of the estimated 5200 annual deaths from food-borne disease (Mead, 1999; Frenzen, 2004). This is of concern since many of today’s commonly recognized food-borne pathogens were not recognized as causes of food-borne illness 30 years ago. In this regard, Mycobacterium avium sub-species paratuberculosis (Map) is an organism of potential concern. Map is the causative agent of Johne’s disease in cattle, but it has been proposed that Map is also the causative agent of Crohn’s disease in humans, and that it may be transmitted via milk (including pasteurized milk) and possibly other foods.
During the 1980s and 1990s, antibiotic-resistant food-borne pathogens emerged that are associated with the inappropriate use of antibiotics in animal husbandry. For example, Salmonella typhimurium DT 104 routinely shows resistance to five different antibiotics. Strains of Salmonella andCampylobacter are showing resistance to fluoroquinolones since these compounds were introduced for use in animals.
In recent years a new range of foods has been implicated with food-borne disease. For instance, the internal contents of an egg were always presumed to be safe to eat raw, and uncooked eggs have been tra-ditionally used in many different food products. This situation has changed with the emergence of S. Enter-itidis infection in egg-laying flocks, resulting in contamination in shell eggs and a major increase in food-borne illness worldwide associated with uncooked eggs. Animal products are no longer the only focus for food safety controls, as fresh produce is emerging as an important vehicle for food-borne disease (McCabe-Sellers and Beattie, 2004). Between 1990 and 2003, 12% of food-borne outbreaks in the USA were linked to produce and produce dishes; the most common produce foods being salads and alfalfa sprouts. Of the produce-associated outbreaks, 40% were due to norovirus or hepatitis A, and 30% were caused by bacteria commonly associated with an animal reservoir, such as Campylobacter, E. coli O157 andSalmonella (Dewaal et al., 2006).
Finally, chemical risks to food, such as pesticide residues, acrylamide, and the use of food additives, continue to concern consumers.