FOOD SAFETY

FOOD SAFETY: A PUBLIC HEALTH ISSUE OF GROWING IMPORTANCE

In recent years the reported incidence of food-borne diseases has continued to increase worldwide, with a number of extremely serious outbreaks occurring on virtually every continent (Kaferstein, 2003). In addition, various high-profile food safety issues, including bovine spongiform encephalopathy (BSE), dioxins, acrylamide, Escherichia coli O157 and Sudan Red 1 have presented themselves to consumers, industry and regulators alike. In a nutritional context, food-borne illness is often associated with malnutrition. In recent times food safety issues have been perceived by the public and governments as posing a greater potential risk to consumer health than nutritional aspects of the diet. To convey positive public health nutritional messages, nutritionists must understand the scientific basis of “food scares” that affect attitudes to food, nutrition, and health. This chapter aims to highlight the reasons for concern about the safety of food, the types and sources of biological and chemical contaminants in foods, and possible control and prevention strategies.

 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).

Changing food supply system

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 processing, longer distribution chains, and new food preparation 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 addition, 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, and move in international 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.

Chronic effects of food-borne illness                                                            

Food-borne diseases are classified as either infections or intoxication. Food-borne infections are caused when viable microorganisms are ingested and these can then multiply in the human body. Intoxication  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 diarrhoea, 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 rheumatoid 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 arthritis. It is estimated that up to 10% of patients with haemorrhagic colitis develop haemolytic uremic syndrome (HUS), a life-threatening complication of Escherichia coli O157:H7 infection characterized by acute renal failure, haemolytic anaemia, and thrombocytopenia.

Vulnerable groups

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 down regulation 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 immunosuppressant drugs, and patients with acquired immune deficiency syndrome (AIDS). In non-industrialized countries, political unrest, war, and famine lead to increased malnutrition and can expose poorer populations to increased risk of food-borne disease.

Emerging food safety issues                                                                               

 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 emerging 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 and Campylobacter 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 traditionally used in many different food products. This situation has changed with the emergence of S. Enteritidis 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 and Salmonella (Dewaal et al., 2006). Finally, chemical risks to food, such as pesticide residues, acrylamide, and the use of food additives, continue to concern consumers.

Food-borne bacteria

The major cause of food-borne diseases is the consumption of microbiologically contaminated foods. There are many types of food-borne pathogens, including bacteria, viruses, and parasites. The characteristics of food-borne bacterial intoxications and infections are summarized in Tables 14.1 and 14.2, respectively. Food-borne pathogens are covered in more detail by Doyle et al. (2001).

Food-borne viruses                                                                                              

 It is only in recent years that the role of viruses as etiological agents of food-borne illness have emerged. Difficulties in attributing viral illness to food have mainly been due to the diagnostic difficulties in detecting viruses in an implicated food and under- reporting owing to the mild nature of illness in many cases. A report from the US Centres for Disease Control (CDC) in 2000, on surveillance of food- borne disease outbreaks from 1993 to 1997, revealed that viruses accounted for 6% of all food-borne out- breaks and 8% of cases. Hepatitis A accounted for the majority of these, followed by norovirus. Data published by the European Food Safety Authority (EFSA) revealed that viruses accounted for 10.2% of all food- borne outbreaks reported during 2006. Caliciviruses (including norovirus) accounted for the majority (61.7%) of these food-borne viral outbreaks. Food-borne viruses are generally enteric, being transmitted by the fecal–oral route. However, transmission by person to person contact and via contaminated water is common. Hepatitis A and norovirus are more commonly transmitted via foods than other food-borne viruses. The most important food-borne viruses are hepatitis A, norovirus, astrovirus, and rotavirus. These are discussed in detail below.

Hepatitis A virus

Hepatitis A is one of the more severe food-borne diseases. The illness results from immune destruction of infected liver cells, and a few weeks of debility are common. It is a member of the picornaviruses. Infections are more likely to be asymptomatic or mild in young children than in adolescents or adults. The virus can be shed in faeces for up to 14 days before the onset of illness. It is therefore possible for an infected food handler with poor personal hygiene (hand-washing, in particular) to contaminate food during this period. The virus may be shed in the faeces for 1–2 weeks after onset of symptoms. Food becomes contaminated with this virus via infected persons or via fecally contaminated water, as is usual with shellfish. Examples of other foods implicated in hepatitis A outbreaks are oysters, raw mussels, drinking water, bakery products and caviar. Hepatitis A has been shown to be more heat resistant than most enteric viruses and is also quite resistant to drying. The virus is susceptible to chlorination treatment, however, and water-borne hepatitis A outbreaks have been linked to untreated water.

Noroviruses

 Norovirus was the first enteric virus reported to be food-borne. It was formerly known as Norwalk-like virus (NLV) or small round structured virus (SRSV) and has recently been classified as a member of the calicivirus family. Noroviruses are difficult to detect, especially from foods.