sign in sign up
<<
Home , Foodborne illness

Foodborne illness

society at large. These costs include loss Economic impact of of income by the affected individual, cost of health care, loss of productivity foodborne illness due to absenteeism, costs of investiga- tion of an outbreak, loss of income due What is damaging and distressing at the to closure of businesses and loss of sales level of the individual also has serious when consumers avoid particular prod- implications on a far larger scale. In de- ucts. In 1989 it was estimated that the veloped countries efforts to quantify the total cost of bacterial foodborne illness economic impact of foodborne illness are to the United States economy was US$ comparatively recent, but it is clear from 6,777,000,000. In developing countries, these that foodborne illness is a major where the problem of diarrhoeal burden on the economy. Costs arise from is far greater, the effect on economic ac- a number of different sources and are tivity and development can only be far incurred both by the individual and by more severe.

KEY POINTS

l is essential for health and well-being.

l Food may also be a cause of illness.

l may be intrinsically toxic or may be contaminated with toxic chemicals or pathogenic organisms.

l Foodborne illness is extensively under-reported.

l (, , moulds and parasites) are the most important cause of foodborne illness.

l Bacteria are generally most important.

l Most foodborne illness is associated with gastrointestinal symptoms of , , pains and diarrhoea.

l Foodborne illness is caused by two mechanisms: and intoxication.

l The infectious dose varies between organisms and between individuals.

l Foodborne illness can have seriously damaging effects on individuals, particularly young children, and on society as a whole.

16 Basic for Health Workers

t t

Food Contamination Diarrhoea Malnutrition t á t

Figure 1.3 The malnutrition and diarrhoea cycle

15 BC - Bronchitis BN - Bronchopneumonia 14 CEL - Cellulitis CONJ - Conjuncivitis Normal growth curve 13 D - Diarrhoea FUO - Fever of unknown origin 12 I - Impetigo M - Measles 11 S - Stomatitis URI - Upper respiratory illness 10 D 9 Child’s growth curve URI D D URI D URI S D 8 D D BN URI BC D URI D D 7 CEL D FUO BC URI URI

Body weight in KG D D D D D D D BC 6 D URI M BC URI URI 5 D I 4

3 CONJ I 2

0 3 6 9 12 15 18 21 24 27 30 33 36 Age in months

Source : Mata, LJ Nutrition and infection. Protein Advisory Group bulletin (1971) Figure 1.4 Growth pattern of a child with frequent episodes of diarrhoea and other (The horizontal bars indicate the duration of the infectious disease)

15 Foodborne illness

Table 1.7 Examples of secondary disease state resulting from foodborne infections Disease Associated complication Brucellosis Aortitis, orchitis, meningitis, pericarditis, spondylitis Arthritis, carditis, cholecystitis, colitis, endocarditis, erythema nodosum, Guillain-Barré syndrome, haemolytic-uraemic syndrome, meningitis, pancreatitis,septicaemia E.coli (EPEC & EHEC types) Erythema nodosum, haemolytic-uraemic syndrome, infections seronegative arthropathy Meningitis, endocarditis, osteomyelitis, abortion and stillbirth, death Aortitis, cholecystitis, colitis, endocarditis, orchitis, meningitis, myocarditis, osteomyelitis, pancreatitis, Reiter’s syndrome, rheumatoid syndromes, septicaemia, splenicabscess, thyroiditis Shigellosis Erythema nodosum, haemolytic-uraemic syndrome, peripheral neuropathy, pneumonia, Reiter’s syndrome, septicaemia, splenic abscess, synovitis Taeniasis Arthritis Foetus malformation, congenital blindness Yersiniosis Arthritis, cholangitis, erythema nodosum, and splenic abcesses, lymphadenitis, pneumonia, pyomositis, Reiter’s syndrome, septicaemia, spondylitis, Still’s disease Source: Mossel, 1988.

foodborne microorganisms (Table 1.7). In for more than 15% of their young lives. an outbreak of salmonellosis in Chicago The immediate cause of death from in 1985, caused by contaminated pasteur- diarrhoeal disease is usually the dehydra- ized , more than 2% of the 170,000- tion that results from the loss of fluid and 200,000 people infected suffered from electrolytes in diarrhoeal stools, but di- as a result of their in- arrhoea can also have other serious fection (3). Guillain-Barré syndrome is a health consequences. It may lead to mal- serious and potentially life-threatening nutrition since food intake is reduced ei- neurological disease characterized by ther as a result of loss of appetite or the acute weakness, autonomic dysfunction withholding of food, and those nutrients and respiratory insufficiency. It is a that are ingested are poorly absorbed or chronic sequela associated with acute simply lost by being swept out with the gastrointestinal infection particularly by diarrhoeal stools. Malnutrition in its turn jejuni. can predispose children to longer episodes of diarrhoea as well as other infections, In developing countries, diarrhoeal aggravating the problem still further. This , particularly infant diarrhoea, are can result in a downward spiral of increas- a major problem. It has ingly poor health which, unless it is bro- been estimated that annually some 1500 ken in some way, will lead ultimately to million children under five years of age premature death (Figure 1.3). Even where suffer from diarrhoea and over 3 million this does not proceed inexorably to a fa- die as a result (4). Individual children ex- tal end, the physical and mental growth perience on average 3.3 episodes of di- of the child is severely impaired. This is arrhoea each year, though in some areas shown in Figure 1.4 which records the the number of episodes may exceed 9 and effect of repeated bouts of diarrhoea and children can be suffering from diarrhoea other illnesses on a child’s development.

14 Basic Food Safety for Health Workers differ appreciably. and limiting indispositions that are restricted enterotoxigenic E. coli (ETEC) are oth- to and are not usually life- erwise very similar organisms but esti- threatening. Exceptions occur with par- mates of their respective infective doses ticularly susceptible individuals such are markedly different, reflecting differ- as the very old or very young, pregnant ences in their . women or those who are already very sick Susceptibility to infection can vary with or weak for some other reason. These a range of factors such as age, general vulnerable groups constitute quite a large health, nutrition, immune status and proportion of the population and for whether a person is undergoing medical many of them diarrhoeal disease can be treatment. Listeriosis can be mild or even fatal. asymptomatic in some individuals but A number of foodborne such can be severe and often life-threatening as botulinum are also associated in the unborn child. In people with low with acute extraintestinal (systemic) gastric acidity, increased survival of disease. C. botulinum causes a severe ingested pathogens can reduce the neuroparalytic syndrome which is often required infective dose, thereby fatal. The mortality rate in outbreaks in increasing the risk of infection. This is the United States between 1976 and 1984 often found in the elderly and may help was 7.5% but it can be substantially explain their increased susceptibility to higher (3). Survival in cases of foodborne infections. The food that is the is critically dependent on early diagnosis vehicle of infection may also help reduce and treatment. the infectious dose by protecting the Sometimes extra-intestinal disease from the lethal effect of the transmitted by food is particularly stomach’s acidity. This has been noted associated with certain susceptible indi- particularly with fatty foods such as sa- viduals. For example, infection by Liste- lami, cheese, chocolate and ice cream ria monocytogenes can vary from a mild, flu- where low numbers of have like illness to meningitis and been implicated in foodborne disease meningoencephalitis. It is particularly outbreaks (Table 1.6). serious in pregnant women; the mother Where the infectious dose is high, the may experience relatively mild symptoms food vehicle can play a very specific role but infection of the fetus can result in in the illness. Depending on the food’s abortion, stillbirth or premature labour. composition and conditions of storage, Listeriosis is also more than 300 times a pathogen present at low and possibly more common in AIDS patients than in harmless levels may grow to numbers the general population. Cancer patients sufficient to produce illness. The speed and other immunocompromised with which bacteria can grow is described individuals are subject to bacteraemia in more detail in Chapter 2. caused by foodborne bacteria. Verotoxin- producing E. coli generally results in a bloody diarrhoea but can cause the Health consequences haemolytic uraemic syndrome, characterized by thrombocytopaenia, of foodborne illness haemolytic anaemia and acute kidney failure, particularly in children. For most adults in the industrialized world, incidents of foodborne illness are Some chronic diseases, particularly ar- unpleasant but are generally mild and self- thritic conditions, can be triggered by

13 Foodborne illness

Since the is ingested with the food This is probably still true in many cases, there is no direct person-to-person spread, but it has been shown more recently that as can occur with some enteric infec- food may also be the vehicle of tions, and the (the time contamination in up to 70% of cases. between consumption of the food and To cause illness, a sufficient number of the appearance of symptoms) tends to cells must be consumed. This is known be shorter, generally of the order of one as the infectious dose. The infectious or two hours or even less in some cases. dose varies from one organism to another This is because the toxin begins to act as and from person to person. For soon as it reaches the site of action, the infectious dose is whereas with infections the microorgan- thought to be quite low, while relatively isms need time to multiply in the body. high numbers of non-typhoid Salmonella There are some similarities here with other are normally required to produce illness. biotoxins such as and algal Experiments have been conducted where , though algae differ from toxigenic volunteers have consumed different lev- bacteria and moulds in that they do not els of pathogens in order to determine multiply in the food. Also, the health ef- the infectious dose. These results and data fects of mycotoxins tend to be long-term from the investigation of actual rather than acute (see Chapter 2). outbreaks give some indication of the numbers of bacteria required to produce illness, but they should be regarded only Infectious dose as a rough guide (Table 1.6). Successful infection is the result of the Infective pathogens can be introduced interaction of two variable factors: the into the body from a variety of sources. virulence of the pathogen (its ability to In the past, it was thought that cause illness) and the susceptibility of the contaminated water was the main source individual. The virulence of different of the pathogens that cause diarrhoea. Salmonella serotypes, for example, can

Table 1.6 Estimated infectious doses

Escherichia coli enteropathogenic 106–1010 enterotoxigenic 106–108 enteroinvasive 108 enterohaemorrhagic 101–103 Shigella 101–102 Salmonella Typhi <103 Other salmonellae 105-107 but: Salmonella Newport 60 – 230 in hamburger Salmonella Eastbourne 10 – 25 in chocolate Salmonella Heidelberg 100 – 500 in cheese 106–108 Campylobacter 500 cholerae 106 105–107

12 Basic Food Safety for Health Workers the normal functions of the gut are up- through the gut. It then multiplies, colo- set in some way. nizing the surface. In some cases, such The or gut is not an as infection with enteropathogenic Es- internal organ of the body but a tube run- cherichia coli, this produces changes in the ning through it where foods are digested gut epithelium which reduce its absorp- and absorbed, and unwanted waste prod- tive capacity or cause fluid secretion. ucts are expelled. In addition to absorp- Colonizing bacteria can also produce tion of nutrients from foods, absorption ; toxins that alter the function and secretion of water are important gut of the cells lining the gut and cause them functions. Water absorption normally to secrete water and electrolytes into the exceeds secretion. Each day, a typical intestine to produce a profuse watery adult will ingest about two litres of wa- diarrhoea. A notable example of this is ter. To this must be added saliva and se- , but a similar sequence of events cretions from the stomach, pancreas and occurs with enterotoxigenic E. coli liver which altogether make a total of 8- infections. 10 litres entering the small intestine daily. Invasive pathogens are not confined to About 90% of this fluid is absorbed be- the intestinal lumen but can penetrate the fore it enters the large intestine where 80- cells lining the gut. In some cases their 90% of the remainder is absorbed. penetration is limited to the immediate Changes in the small intestine that either vicinity of the gut, as with the non-ty- decrease absorption or increase secretion phoid . Some pathogens in- will reduce overall absorption and result vade the mucosa of the large intestine in a larger fluid flow into the large intes- rather than the small intestine, producing tine. If this exceeds the relatively limited inflammation, superficial abscesses and absorptive capacity of the large intestine ulcers, and the passage of dysenteric then diarrhoea occurs. stools containing , pus and large amounts of mucus. In other cases, Bacteria cause foodborne illness by two microbial invasion is not restricted to the mechanisms: infection and intoxication. gut’s immediate locality and the organ- The latter can also be caused by chemi- ism spreads further through the body, cal contaminants and naturally occurring producing symptoms other than diarrhoea toxins. at sites remote from the gut itself, as for example in brucellosis, listeriosis, typhoid Infection and paratyphoid fevers. Infection occurs when living bacteria are Illnesses caused by foodborne viruses ingested with food in numbers sufficient and parasites are also broadly similar in for some to survive the acidity of the that viable organisms gain access to their stomach, one of the body’s principal pro- site of action in the body via the tective barriers. These survivors then pass gastrointestinal tract. into the small intestine where they mul- tiply and produce symptoms. Intoxication Infections can be invasive or non-inva- With foodborne intoxications, the bac- sive. In non-invasive infections, the or- teria grow in the food producing a toxin. ganism attaches itself to the gut surface When the food is eaten, it is the toxin, or epithelium to prevent itself from being rather than the microorganisms, that washed out by the rapid flow of material causes symptoms.

11 Foodborne illness

figures are collected, but it is thought to n Changing lifestyles also means that reflect an underlying increase in the food preparation may be in the hands number of cases as well. of the relatively inexperienced as A number of factors have contributed to more mothers go out to work and this trend. Their relative importance var- more people eat pre-prepared foods, ies between countries and between patho- meals from catering establishments or gens but some of the most significant are food from street vendors. as follows: n An increasing proportion of the popu- lation is more susceptible to n Increasing industrialization and urban living has meant that the food chain foodborne illness. This includes the has become longer and more complex, malnourished, the elderly, those who increasing opportunities for contami- have some underlying condition such nation. It also means that more peo- as liver disease and those who are ple are likely to be affected by a sin- immunocompromised as a result of gle breakdown in food . infections such as HIV and immuno- suppressive medical treatment. n In poorer countries increased urbani- zation and rapid population growth have not been matched by develop- ment of the health-related infrastruc- Foodborne illness: ture, including basic sanitation, and this has led to increased risk of con- its definition and tamination of the food and water sup- ply. nature

n Increasing affluence in other areas has The term “food ” has often been led to greater consumption of foods used in some countries, but it is an ex- of animal origin such as meat, milk, pression that can sometimes be restric- and eggs. These foods are rec- tive or misleading. Foodborne illness or ognized as more common vehicles of foodborne disease are now the generally pre- foodborne pathogens and this situa- ferred terms. Foodborne disease can be tion can be exacerbated by the meth- defined as: ods of intensive production required “any disease of an infectious or toxic to supply a larger market. nature caused by or thought to be n There is greater international move- caused by the consumption of food ment of both foods and people. Ex- or water”. otic Salmonella serotypes have been Though there are a number of important introduced into Europe and the exceptions that will be described later, United States as a result of the im- in most cases and in most people’s minds, portation of animal feeds. A number the illnesses caused by foodborne micro- of outbreaks of illness associated with organisms, principally bacteria, are asso- imported foods have also been re- ciated with gastrointestinal symptoms of corded. Tourism is one of the world’s nausea, vomiting, stomach pains and di- major growth industries and every year arrhoea. Since diarrhoea is a common more and more people travel abroad clinical symptom in foodborne diseases, where they are exposed to increased many of these diseases are referred to as risk of contracting foodborne illness. “diarrhoeal diseases”. These occur when

10 Basic Food Safety for Health Workers foodborne in origin or may not be re- cases being reported. Studies in some ported to the relevant authority for re- countries point to an under-reporting cording. Estimates vary but it is gener- factor of up to 350 in some cases. ally believed that in developed countries less than 10%, or even only 1%, of cases Statistics from both developed and de- of foodborne illnesses ever reach official veloping countries show an increasing statistics. In countries with fewer re- trend in foodborne illness over recent sources, under-reporting must be even years (Figure 1.2). In part, this is prob- greater, with probably less than 1% of ably due to improvements in the way the

90000

80000

70000

60000 Notifications 50000

40000

30000 1989 1990 1991 1992 1993 1994 1995 1996 Year Figure 1.2a Foodborne illness : annual notifications, England and Wales

180

140

120

100

80

60

40 Cases per 100,000 population 20

0 1976 1978 1980 1982 1984 1986 1988 1990 1992 1994 Year

Figure 1.2b of foodborne disease in Venezuela

9 Foodborne illness

DDT complex (DDT and its degradation products) contaminates food mainly as a result of its earlier use in and public health. While DDT is now banned in most countries for agricultural uses, the persistence and fat solubility of DDT have resulted in widespread contamination of the food chain. Levels of DDT in breast milk reflect the exposure of the mother to DDT and is a good indicator of the levels of DDT in the food supply. Breast milk is also the sole food for the first few months of life and dietary intake of DDT complex by infants in some countries approaches or exceeds the WHO recommended provisional tolerable intake of 20 mg DDT/kg body weight/day. Source: GEMS/Food WHO document (WHO/FSF/FOS/97.9) Figure 1.1 Dietary intake of DDT by infants from human milk

Data collected by the Food Contamina- A number of human viruses can be trans- tion Monitoring and Assessment Pro- mitted by food and human diseases gramme (GEMS/Food) indicate that in caused by , helminths and nema- many countries the trend in chemical todes that are animal parasites are prob- contaminant levels is generally down- lems of emerging importance in a wards. This is most apparent in developed number of countries. These differ from countries where exposure to these most bacterial foodborne illnesses in that contaminants is often much lower than the causative organism does not multi- in developing countries (Figure 1.1). ply in the food itself. A brief description Factors contributing to this disparity are of the major foodborne pathogens and discussed in Chapter 2. The general over- some of their key features is presented all improvement is due to increased re- as Appendix 1. Most of the following is striction of the use of toxic chemicals concerned primarily with bacterial patho- and that persist in the environ- gens, though specific aspects of other ment, and improved control of environ- pathogens are mentioned where appro- mental . Available data on priate. foodborne illness of biological origin pro- vide a strong contrast to this reduction in chemical contamination. Extent of foodborne Several different types of organism can cause foodborne illness. Bacteria, single- illness celled organisms with typical dimensions of around 1mm (10-6m), are the most im- Many developed countries have sophis- portant and well studied foodborne ticated systems for collecting data on the pathogens. A key factor is their ability to incidence and causes of foodborne illness. multiply in food, thus increasing the haz- Yet it is known that these data represent ard they pose. This is discussed in Chap- only a fraction of the number of cases ter 2. Filamentous fungi (moulds) can also that occur. Infected individuals may not grow in foods and some produce toxic seek medical advice, and if they do their substances called mycotoxins. illness may not be recognized as

8 Basic Food Safety for Health Workers

Table 1.4 Mean daily intakes (mg) of natural food Class of compound (food source) Population Total Vegetarian

Glucosinolates (brassicas) 50 110 Glycoalkaloids (potatoes) 13 70 - 90 Saponins (legumes) 15 100 (*220) Isoflavones (soya) <1 105

* U.K. vegetarian population of East African origin Source: Morgan, MRA. and Fenwick, GR National foodborne toxicants. Lancet, 15 December 1990, p. 1492/1495. In most cases foods are not contaminated with residues, environmental intentionally but rather from carelessness chemical contaminants and the use of food or insufficient education or training in food additives cause most concern. Yet experi- safety. In some cases, contamination may ence shows that most outbreaks of be deliberate as, for example, in the mis- foodborne disease are associated with use of food additives such as prohibited microbiological contamination. colouring. In one serious case in Spain, con- This is reflected in the available statistics taminated industrial rapeseed oil was sold on the etiology of foodborne illness. for human consumption, killing more than (Table 1.5). One study estimated that 500 people and crippling more than 20,000 people are 100,000 times more likely to (1). become ill as a result of microorganisms How the relative importance of these haz- in food than as a result of pesticide ards is perceived depends on who you ask. residues (2). Surveys indicate that, as far as the general public is concerned, hazards associated

Table 1.5 Etiology of foodborne disease outbreaks (with known etiology) in Latin America and the Caribbean, 1995-1997 Etiological agent Percentage Percentage of cases involved of outbreaks in outbreaks Bacteria 46.3 83.03 Of which: cereus 1.3 1.2 Clostridium perfringens 4.2 4.1 0.4 0.1 11.4 7.8 Salmonella 37.0 43.1 Shigella spp. 3.1 21.9 Staphylocccus aureus 36.6 19.5 4.2 0.9 Vibrio parahemolyticus 0.2 0.4 Other 1.6 1.0 Total 100.0 100.0 Viruses 1.8 3.7 Parasites 1.8 2.9 Marine toxins 44.2 8.0 Plant toxins 0.4 0.1 Chemical substances 5.4 2.3 Total 100.0 100.0 Source: Adapted from data provided by the Pan American Institute for Food Protection and Zoonoses, INPPAZ, PAHO/ WHO 1998

7 Foodborne illness

Table 1.2 Examples of vitamin and mineral deficiency syndromes

Micronutrient Deficiency syndrome A Night blindness, xeropthalmia Thiamine Beriberi, Wernicke’s encephalopathy; Korsakoff’s psychosis Niacin Pellagra Riboflavin Mucosal lesions Pyridoxine Glossitis, neuropathy Folate Megaloblastosis, villus atrophy

B12 Pernicious anaemia, megaloblastosis, neuropathy C D Rickets, osteomalocia K Hypoprothrombinaemia Iodine Goitre, cretinism Iron Anaemia

and established processing and handling Other foodborne hazards can be described procedures are followed, the majority do as extrinsic, indicating that their presence not cause serious problems. Natural food is a result of contamination of the food. toxins are described in more detail in This includes contamination with indus- Chapter 2 but a few examples are given trial chemicals or pesticide residues, right in Table 1.3 and estimates for some mean through to the presence of pathogenic bac- daily intakes in the are teria or parasites. The range of possibili- presented in Table 1.4. ties is summarized in Table 1.3. Table 1.3 Causes of foodborne illness Examples INTRINSIC HAZARDS (Natural Toxins or Antinutritional Factors) oxalic acid (rhubarb, spinach) (potatoes) dioscorine (yams) (cassava, lima ) haemagglutinin (red kidney beans) protease inhibitors (legumes) phytic acid (bran) amatoxin, psilocybin and others (toxic mushroom) EXTRINSIC HAZARDS Chemical Contamination dioxins, PCBs heavy metals cadmium mercury lead pesticide residues Biological Contamination Bacteria causing infection e.g. Salmonella causing intoxication e.g. C. botulinum Parasites helminths e.g. roundworms protozoa e.g. lamblia Viruses e.g. , Small Round-Structured Viruses (SRSVs) Fungi/mycotoxins e.g. Algae (e.g.dinoflagellates leading to paralytic )

6 Basic Food Safety for Health Workers

Chapter 1 Foodborne illness

Food in health and disease

Food is essential both for growth and for Even when a diet provides enough pro- the maintenance of life. It supplies the tein and energy, it may not supply suffi- energy and materials required to build cient essential minerals or vitamins and and replace tissues, to carry out work and may thus give rise to characteristic defi- to maintain the body’s defences against ciency disorders (Table 1.2). disease. Illness can also result from what a food Food can also be responsible for ill-health. contains rather than from what it lacks. Failure to consume enough of the right kind Some hazards of this kind are described of food will impede growth and impair as being intrinsic to the food in the sense health. For example, protein-energy that they are normal and natural constitu- malnutrition can lead to a range of clinical ents of the food. Many common food manifestations. These vary from marasmus, plants, for instance, contain toxic com- where consumption of protein, dietary pounds designed to deter predators or energy and other nutrients are chronically invading microorganisms. Their intake is reduced, to kwashiorkor (sometimes inevitably higher in those people with a thought to be associated with an over- largely vegetarian diet. reliance on low protein staples) which results in a quantitative and qualitative However, in most cases where the food deficiency of protein (Table 1.1). supply is generally varied and plentiful,

Table 1.1 Classification of severe protein-energy malnutrition in children Weight for age* With oedema Without oedema 60 –80% Kwashiorkor Undernutrition Less than 60% Marasmic kashiorkor Marasmus

* As % of standard (National Centre for Health Statistics) weight Source: Tomkins, AM Nutrition in clinical . In: Textbook of Medicine. RL Souhami and J Maxham (eds) 2nd edn. Churchill Livingstone, Edinburgh, 1994: p.106.

5