PhD Lecture 1 PDF - University of Baghdad

University of Baghdad College of Veterinary Medicine Dept. of Vet. Public Health/ Food Hygiene Important Facts in Foodborne Diseases I. INTRODUCTION The objective of this topic is to recognize the causes of...

University of Baghdad College of Veterinary Medicine Dept. of Vet. Public Health/ Food Hygiene Important Facts in Foodborne Diseases I. INTRODUCTION The objective of this topic is to recognize the causes of foodborne diseases, the role of microorganisms and several other agents in foodborne diseases, and the sim importance of predisposing factors in the occurrence of a foodborne disease. This information will help not only understand the epidemiology of foodborne diseases but also develop means of controlling them. II. HUMAN GASTROINTESTINAL DISORDERS.Ja The causes of foodborne gastrointestinal disorders can be broadly divided into three groups: aN 1. From consumption of food and water containing viable pathogenic microorganisms or their preformed toxins. 2. From ingestion of pathogenic algae, parasites, and their preformed toxins through ud food. 3. For reasons other than viable pathogens or their toxins..H Some of the factors included in Group 3 are: Dr 1. Ingestion of toxins naturally present in many foods. This includes certain mushrooms, some fruits and vegetables, and some seafoods. 2. Toxins formed in some foods. Examples are some biological amines (e.g., histamine) that form in some fish, cheeses, and fermented meat products. 3. The presence of toxic chemicals in contaminated food and water, such as heavy metals and some pesticides. 4. Allergy to some normal components of a food. Some individuals are allergic to gluten in cereals and develop digestive disorders following consumption of food containing gluten. 1 5. Genetic inability to metabolize normal food components. The inability of some individuals to hydrolyze lactose in the small intestine, because of the lack of production of the enzyme lactase, results in digestive disorders (lactose intolerance). 6. Indigestion from overeating or other reasons. The incidence of foodborne diseases of microbial origin is higher than that for all others causes combined. In the U.S., among the total number of cases reported of foodborne disease outbreaks, pathogenic microorganisms caused 94.4%, and only 1.1% and 4.3% were caused by parasites and chemicals, respectively. Even at present, the occurrences of foodborne diseases caused by pathogenic microorganisms far exceed those by all others combined. In recent years, foodborne sim diseases of microbial origin have become the primary food safety concern among U.S. consumers and regulatory agencies. This trend is probably true in most other developed and developing countries.1 III. EPIDEMIOLOGICAL ASPECTS Investigation of a Foodborne Disease.Ja In general, various regulatory agencies at the local, state, and national levels are aN empowered with the responsibility of investigating the cause of a reported foodborne disease. In the U.S., the regulatory agencies involved in the investigation of a foodborne disease are the local health department; state health, food, and agriculture departments; the federal Food and Drug Administration (FDA); U.S. ud Department of Agriculture (USDA); Centers for Disease Control and Prevention (CDC); and several others. Initially, a medical doctor who suspects a patient to have a foodborne disease informs the local or state health officials about the incident..H These agencies, following a preliminary investigation and recognizing the cause to be of food origin, report the incident to the appropriate federal agencies, which then conduct an epidemiological investigation. The investigation at the state and federal Dr levels involves examination of the suspected foods, environmental samples, and materials obtained from the patients for pathogens, microbial and non microbial toxins, and chemicals. Results of these tests provide direct evidence of the association of an agent (e.g., pathogen, toxin, parasite, chemicals) with the disease. In addition to testing suspected samples, both the sick and other people who consumed the same food from the same source are interviewed to establish an indirect association of the most likely foods with the disease. This information is collected, recorded, and reported by the CDC,. Foodborne Disease Outbreak 2 In the U.S., the federal regulatory agencies define a foodborne disease as an outbreak when two or more people become sick with a similar illness (symptoms) from the consumption of the same food from the same source, and the epidemiological investigations implicate, either directly or indirectly, the same food from the same source as the cause of the illness. However, in the case of botulism, because of a high fatality rate, even when only one person has the illness, it is considered an outbreak. For chemical poisoning too, even a single case is considered an outbreak. Incidence of Foodborne Disease Outbreak The incidence of foodborne illnesses in most of the developed countries is lower than in many developing countries. The major reasons for the low incidence are the sim implementation of necessary regulations in production and handling of foods, good sanitary practices, and the availability of necessary facilities to reduce abuse. In the U.S., an average of 479 foodborne disease outbreaks were reported each year,. However, on average, only 38% of the outbreaks, were confirmed. This shows that.Ja even for the reported incidents, only some could be confirmed from the direct evidence. It is suspected that even in the developed countries, only a small fraction of the total incidents are reported. In many instances, an individual does not consult aN a doctor, and even if a person does consult a doctor, the incident might not be reported to the regulatory agencies. Based on the mechanisms involved in the surveillance system, it is estimated that in the U.S., 5 million individuals are affected by food- and waterborne diseases every year. ud Cost of Foodborne Diseases Foodborne illnesses can be fatal as well as cause suffering, discomfort, and debilitation among the survivors. The economic losses from various factors, such as.H medical treatment, lawsuits, lost wages and productivity, loss of business, recall and destruction of products, and investigation of the outbreaks, can be very high. In the Dr U.S., the annual cost of foodborne diseases is estimated to be more than $20 billion. Costs were estimated from foodborne illnesses from seven pathogens (Campylobacter jejuni, Clostridium perfringens, Escherichia coli O157:H7, Listeria monocytogenes, Salmonella, Staphlococcus aureus, and Toxoplasma gondii). Predominant Etiological Agents As indicated before, gastrointestinal disorders can be caused by the consumption of food and water containing pathogenic microorganisms and their toxins; pathogenic algae and parasites and their toxins; toxic chemicals, either natural or as a contaminant; and by other factors. Among these, the largest number of outbreaks, the total number of cases, and the number of deaths are caused by pathogenic 3 bacteria and their toxins. U.S., bacteria caused 66% of the outbreaks affecting 92.2% of the cases and 96.4% of the fatalities. Outbreaks caused by viruses, parasites, and chemicals were 4.5, 4.0, and 25.5%, respectively. Results of a similar U.S. study showed that percentages of foodborne disease outbreaks and cases, respectively, were as follows: bacterial, 66.3% and 90.9%; viral, 2.7% and 3.5%; parasitic, 7.8% and 1.1%, and chemical 23.5% and 4.3%. This report did not include the number of fatalities. Both reports indicated that pathogenic bacteria are the major cause of foodborne diseases in the U.S. This is probably also true for other countries. Current information for recent years, presented later, also shows the same trend. Several factors might be responsible for the high incidence caused by pathogenic bacteria: many pathogenic bacteria are found in the raw food materials of animal and plant origin, many are present in the food environments, many grow very effectively in sim different foods, and many are not killed by the conditions used for processing of different foods. Types of Microbial Foodborne Diseases.Ja Foodborne diseases in humans result from the consumption of either food and water contaminated with viable pathogenic bacterial cells (or spores in the case of infant botulism) or food containing toxins produced by toxigenic bacteria and molds. aN On the basis of mode of illnesses, these can be arbitrarily divided into three groups: intoxication or poisoning, infection, and toxicoinfection. 1. Intoxication ud Illness occurs as a consequence of ingesting a preformed bacterial or mold toxin because of its growth in a food. A toxin has to be present in the contaminated food. Once the microorganisms have grown and produced toxin in a food, there is no need of viable cells during consumption of the food for illness to occur. Staph food.H poisoning is an example. 2. Infection Dr Illness occurs as a result of the consumption of food and water contaminated with enteropathogenic bacteria or viruses. It is necessary that the cells of enteropathogenic bacteria and viruses remain alive in the food or water during consumption. Viable cells, even if present in small numbers, have the potential to establish and multiply in the digestive tract to cause the illness. Salmonellosis and are examples. 3. Toxicoinfection 4 Illness occurs from ingesting a large number of viable cells of some pathogenic bacteria through contaminated food and water. Generally, the bacterial cells either sporulate or die and release toxins to produce the symptoms. Clo. Perfringens gastroenteritis is an example. In addition to the pathogenic microorganisms associated with foodborne illnesses, some bacterial species and strains normally considered nonpathogenic can cause gastroenteritis, especially in susceptible individuals. They are designated as opportunistic pathogens. They are normally required to be alive and present in large numbers when consumed through a contaminated food. Predominant microorganism Associated with Foodborne Diseases Although many pathogenic bacterial species and viruses have been implicated with sim foodborne (and waterborne) disease outbreaks, some have occurred at a higher frequency than others. Of the two most common pathogens associated with foodborne intoxication, the number of deaths was higher for Clo. botulinum, but the total number of cases was much higher for Sta. aureus. Among the enteric.Ja pathogens, the largest number of outbreaks, cases, and fatalities resulted from foodborne infections caused by Salmonella. Toxicoinfection outbreaks and number of cases were higher for Clo. perfringens than for Bacillus cereus. Of the two most aN common viral diseases from contaminated food and water, the number of outbreaks was higher for hepatitis A, but Norwalk-like viruses affected more people. salmonellosis was associated with the highest number of outbreaks of all foodborne diseases, affecting the largest number of individuals and causing the most deaths. In contrast, botulism affected the least number of people but caused the highest ud number of deaths in the affected people. No death was reported from staphylococcal intoxication, Bac. cereus gastroenteritis, or Norwalk-like viral infection. Some reasons for higher incidence of some pathogens, such as Salmonella,.H over others can be their occurrence in higher frequency in the food environments, their greater ability to produce the disease, and their ability to grow more rapidly Dr under abusive conditions. Predominant Food Types Associated with Foodborne Diseases Certain food types or foods prepared under specific conditions and environments have been implicated more frequently with foodborne disease than others. Some of the factors could be the presence of a pathogen in the raw materials in higher frequency, thereby having a greater chance to contaminate the finished products, the ability of a pathogen to grow advantageously in a particular type of food, a 5 greater chance of failure in quality control in a specific environment, and a higher possibility of food handlers to contaminate the finished products. Some of these aspects can be explained from the foodborne disease outbreak.Foods of animal origin (meat, fish, eggs, and dairy products) were implicated in 23% of the outbreaks, and Salmonella serovars were involved in large proportions (except for fish); the latter may arise because many food animals harbor Salmonella as carriers in the digestive tract and can thus contaminate meat, eggs, and dairy products. In fish products, the incidence of botulism outbreaks was high, because they can be contaminated with Clo. botulinum present in some marine environments. In recent years, fish consumption has increased and so have the foodborne disease outbreaks from fishery products. Similarly, fruits and vegetables can be contaminated with Clo. botulinum from the soil. In contrast, salads, which are handled extensively, can be sim contaminated with several pathogens of human origin. The food types in 40% of the outbreaks could not be determined, because the food samples were not available for testing in many cases. However, one can speculate from the high incidence of Salmonella in both multiple food and unknown food categories that many were probably foods of animal origin..Ja Predominant Places of Food Consumption Associated with Confirmed Foodborne Disease Outbreaks aN An analysis of the relationship between the places of food consumption and the number of foodborne disease outbreaks revealed that, at least in the U.S., the highest number of incidents occurred with foods served at food establishments These include fast-food services, restaurants, cafeterias, and schools. Several factors ud can be associated with this. The total number of meals served is very high. Also, high proportions of food are served within a very short period of time. In addition, the number of people involved in handling the food, many of whom may not have.H training in safe food handling, is very high. This can result in a greater chance of contamination and failure to observe proper sanitation. Improper cooling of foods, Dr cross-contamination, and contamination of food from pets can be the reasons for foodborne diseases with foods served in homes. Mishandling of foods, temperature abuse, long intervals between preparation and consumption, and improper sanitation can be associated with outbreaks at picnics. The exact sources could not be identified in 30% of the outbreaks; from the available information, it is most likely that many of them were probably with foods served at food establishments. the relative frequency of foodborne disease outbreaks with foods from large commercial processors is low. This is generally because they use good quality control, sanitation, and testing of the products for the pathogens. However, when a contamination of food by a pathogen occurs in a big processing establishment, a large number of people over a wide area are affected. 6 Predominant Contributing Factors Associated with Confirmed Foodborne Disease Outbreaks Before foods are consumed, they are exposed to many different environments and conditions. These dictate whether a pathogen present initially will survive or be killed, if recontamination can occur, or if a pathogen can multiply to reach a high population to cause disease. The foodborne disease outbreak in the U.S. revealed that the most predominant cause of the outbreaks was improper holding temperature (refrigerated temperature) of the food. The temperature abuse resulted in the growth of pathogens (bacteria) to reach to a level that causes illness following consumption. The other factors, in order of importance, were contamination of foods due to poor personal hygiene, survival of pathogens due to cooking at lower temperatures than specified, cross-contamination of foods from sim equipment (previously contaminated with pathogens), and food from unsafe sources, such as raw foods. These five factors, in combination, were responsible for 92.6% of the outbreaks caused by pathogenic bacteria and viruses..Ja Influence of Month (of the Year) on Number of Foodborne Disease Outbreaks In general, foodborne outbreaks of pathogenic bacterial and viral origin are more prevalent during the summer months. in the U.S., 66% of the outbreaks occurred aN during May to September, with the highest incidence in August. Between November and April, the incidence was reduced to 34%. During commercial processing, food products are exposed to indoor temperature, which may not vary greatly in the summer or the winter. However, both raw products and processed products can be ud exposed to outside temperatures for a long time during transportation, displays in stores, at food establishments, and at home. Also, during the summer, picnics and outdoor eating occur more frequently. A high temperature during the summer can.H stimulate rapid growth of the contaminating pathogens to reach a high level, even from a low initial level, within a relatively shorter period. During the winter months, the growth rate can be greatly reduced. Dr Influence of Location on Foodborne Diseases In general, the incidence of foodborne disease outbreaks is lower in the developed countries than in the developing countries. Several socioeconomic reasons and climatic conditions cause this difference. However, the frequency of outbreaks can vary greatly among regions, both in the developed and developing countries. In the U.S., foodborne disease outbreaks have been recorded more frequently in some states than in others. States with high populations, , and warm climates have more incidents. States in this group are New York, Washington, California, Hawaii, and Pennsylvania. a large population, greater frequency of migration and traveling of 7 people, can cause a high incidence rate. In comparison, states with lower populations had very few incidents. Human Factors in Foodborne Disease Symptoms When a group of people consumes food contaminated with live cells of pathogens or their toxins, all the members might not develop disease symptoms. Among those who develop symptoms, all might not show either the same symptoms or the same severity of a symptom. This is probably due to the difference in resistance among individuals. One of the factors involved in developing symptoms from the consumption of a contaminated food is susceptibility of an individual to the contaminants. In general, infants and old, sick, and immunodeficient people are more susceptible than normal adults and healthy individuals. The chance of sim developing disease symptoms is directly related to the amount of a contaminated food consumed. This is related to the number of viable cells of a pathogen or the amount of a toxin consumed by an individual. The virulence of a pathogen or a toxin consumed through a food also determines the onset of a disease and severity of.Ja symptoms. For some highly virulent pathogens, such as Esc. coli O157:H7, consumption of as low as ten viable cells can cause disease in an infant. In contrast, for some pathogens, such as Yersinia enterocolitica, consumption of as high as 1 aN million or more viable cells is necessary for the symptoms to develop. Acceptance Quality of Food Because of Growth of Pathogens Pathogenic viruses need viable host cells for growth; thus they cannot grow in ud prepared foods, and do not affect the food quality. Pathogenic bacteria can grow in many foods. When the environment is suitable, only a few viable cells present initially can reach a high level, maybe several millions per gram or milliliter. However, growth of some pathogens, even to a high level, may not alter the color,.H texture, and odor of a food (such as Sta. aureus). People can consume this food unknowingly and develop symptoms of a foodborne illness. Dr Sequence of Events in a Foodborne Disease For a foodborne disease to occur, several events have to happen in sequence. Understanding these sequences is helpful to investigate the cause (source and means of transmission) of a foodborne disease. It also helps recognize how the sequence can be broken in order to stop a foodborne disease. Initially, there has to be a source of a pathogen. Next, the pathogen has to contaminate a food. Consumption of the food contaminated with a pathogenic virus can lead to viral infection. For bacterial pathogens (and toxicogenic molds) the contaminated food has to support growth and be exposed for a certain period of time at a suitable temperature to enable the pathogens to grow. However, for some potent pathogens 8 (such as Esc. coli O157:H7), growth may not be necessary to cause a foodborne infection. For intoxication, growth should reach a sufficient level to produce enough toxin so that when the food is consumed, the individual develops the symptoms. For bacterial infection, viable cells of a pathogen need to be consumed in sufficient numbers, which vary greatly with pathogens, to survive stomach acidity, establish in the digestive tract, and cause illness. Foodborne Disease Outbreaks the incidence of outbreaks, number of cases, and number of deaths declined, but were still higher. the incidence of illnesses was highest from foods of animal origin and occurred more frequently during May to October, with the highest incidence during June to August. Similarly, , homes (15.2%) and food services (35.7%) were the sim major sources of foodborne illness. Among the pathogens, the incidence was the highest with Salmonella, 65.4%; Serovar Enteritidis was the predominant isolate. the three major contributing factors for the outbreaks remained essentially the same, namely, improper holding temperature, poor personal hygiene, and contamination) increased slightly. Estimated Foodborne Illnesses.Ja inadequate cooking. The frequency of contaminated equipment (including cross- aN For a long time, opinions differed on the actual number of foodborne illness cases vs. the number of cases reported annually in the U.S. Recently, a group of researchers published a report on the estimated number of cases of foodborne ud illnesses from both known and unknown causes. the total number of foodborne illnesses from known and unknown causes was estimated to be 76 million annually, with 325,000 hospitalizations and 5000 deaths in the U.S. Among these, the known pathogens account for an estimated 14 million illnesses, 60,000 hospitalizations, and.H 1800 deaths. About 75% of these deaths were caused by Salmonella, Listeria, and Toxoplasma. The report indicated that via different surveillance programs, an Dr accurate number of illnesses associated with outbreaks caused by some pathogens was available. 9