9. Foodborne Diseases and the Investigation of Disease Outbreaks

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9. Foodborne Diseases and the Investigation of Disease Outbreaks

Study Session 9  Foodborne Diseases and the Investigation of Disease Outbreaks 3

Introduction 3

Learning Outcomes for Study Session 9 3

9.1  Overview of foodborne diseases 3

9.2  Transmission of foodborne diseases 4

Question 4

Answer 4

9.3  Classification of foodborne diseases 4

9.3.1  Food poisoning 5

9.3.2  Food infection 6

9.3.3  A catalogue of foodborne diseases 6

Question 6

Answer 6

Question 6

Answer 7

9.4  Selected examples of common foodborne diseases in Ethiopia 7

9.4.1  Bacterial infections 7

9.4.2  Viral infections 7

9.4.3  Tapeworms 7

Beef tapeworm 8

Dog tapeworm 8

Fish tapeworm 8

9.4.4  Bacterial food poisoning 9

Staphylococcal food poisoning 9

Botulism 9

9.4.5  Chemical food poisoning 9

Pesticides 9

Heavy metals 9

9.5  General management of foodborne diseases 10

9.6  Investigation of foodborne disease outbreaks 11

Box 9.1  Steps in investigating a foodborne disease outbreak 11

Summary of Study Session 9 12

Self-Assessment Questions (SAQs) for Study Session 9 12

SAQ 9.1 (tests Learning Outcomes 9.1 and 9.2) 13

Answer 13

SAQ 9.2 (tests Learning Outcome 9.2) 13

Answer 13

SAQ 9.3 (tests Learning Outcome 9.3) 13

Answer 14

SAQ 9.4 (tests Learning Outcome 9.4) 14

Answer 14

Appendix 9.1 14

Study Session 9  Foodborne Diseases and the Investigation of Disease Outbreaks


Foodborne diseases are a major public health problem. They result from eating foods that contain substances which are either infectious or toxic in nature. In the previous session you have learned about microbial and chemical food contamination. In this session you will learn more about the foodborne diseases that are important for public health, their type and classification, their characteristics and their common symptoms. You will also learn how outbreaks of foodborne diseases should be investigated.

Learning Outcomes for Study Session 9

When you have studied this session, you should be able to:

9.1  Define and use correctly all of the key words printed in bold.

(SAQ 9.1)

9.2   Describe the main types and classification of foodborne diseases. (SAQs 9.1 and 9.2)

9.3  Describe and give examples of the most common bacterial, viral and parasitic foodborne diseases. (SAQ 9.3)

9.4  Describe how you can conduct investigations of foodborne disease outbreaks. (SAQ 9.4)

9.1  Overview of foodborne diseases

Since as far back as the time when the documentation of human history began, consumption of contaminated food and foodborne diseases have been a major global health problem. Contamination can be with microorganisms, chemicals and physical objects in food (as you learned in Study Session 8), which can lead to a variety of foodborne diseases or ill effects such as poisoning.

Foodborne diseases are still a major public health concern all over the world today. They are responsible for many cases of adult illnesses and some deaths, but more importantly, contaminated food is a source of the acute diarrhoeal diseases that claim the lives of enormous numbers of children every day. Worldwide, about 2 million children under the age of five years die from diarrhoeal diseases every year.

In developing countries like Ethiopia, the problem reaches great proportions for many reasons. Most basic among these are poverty and a lack of public health awareness. The problem of foodborne disease is more serious among rural communities where there tends to be a lower level of awareness about the causes and prevention of foodborne infection.

Well-documented information is lacking regarding the extent of foodborne diseases in Ethiopia because many cases are not properly diagnosed or not reported, and many people who are sick with foodborne diseases do not visit health facilities. This makes it difficult to collect statistical data or even make an estimation of the level of the problem – except that it is certainly huge.

9.2  Transmission of foodborne diseases

In the two previous study sessions you have learned about microorganisms and food contamination. The single method of transmission of foodborne diseases to human beings is through ingestion (eating) of food in the following categories:

  • Raw or undercooked meat and meat products

  • raw milk (that is, milk that has not been pasteurised or sterilised)

  • food items contaminated with human faeces (directly or indirectly)

  • raw vegetables contaminated with soil

  • food contaminated by chemicals, e.g. pesticides such as malathion

  • food prepared using contaminated water, e.g. for washing vegetables

  • food kept in an unsuitable condition for a long time after preparation

  • poisonous plants.


Why is it unwise to eat food that has been kept for a long time after it was prepared?


It may have been kept in conditions that created a favourable environment for the growth and multiplication of microorganisms in the food, especially if it was exposed to flies, cockroaches, etc., or kept at a warm temperature.

End of answer

9.3  Classification of foodborne diseases

Foodborne diseases are usually classified on the basis of whatever causes them. Accordingly they are divided into two broad categories: food poisoning and food infections. Each of these categories is further subdivided on the basis of different types of causative agent (see Figure 9.1). We will discuss each of them in turn.

Figure 9.1  Classification of foodborne diseases.

9.3.1  Food poisoning

Food poisoning can be from chemical or biological sources. If we eat food that contains harmful chemicals, or biological toxins (poisons) from plants, animals or microorganisms, that food can make us sick. Some common sources of food poisoning are caused by contaminants already in the food when the raw materials are harvested, for example:

  • Bacterial toxins produced by bacteria such as Clostridium botulinum and Clostridium perfringens, which are commonly found in the natural environment, e.g. in soil.

  • Chemical toxins, e.g. insecticides sprayed onto growing crops.

  • Heavy metals, e.g. lead and mercury, particularly in fish caught near chemical processing facilities.

  • Certain toxic plant tissues, e.g. poisonous mushrooms.

  • Toxic animal tissues, e.g. the poison glands of certain fish, crabs, etc.

Chemical food poisoning can also occur if foodstuffs have been in contact with toxic chemicals during food production, processing, storage and handling.

The symptoms of food poisoning can range from mild headache to severe flu-like symptoms. The most common signs and symptoms are nausea, stomach cramps, diarrhoea, fever, chills and vomiting. A person with food poisoning may have any combination of these symptoms depending on the cause or the agent involved. The illness may begin from 1 to 72 hours after eating the food.

9.3.2  Food infection

The diagnosis, treatment and prevention of all these diseases are covered in more detail in the Module on Communicable Diseases.

Food infection occurs as a result of ingestion of pathogenic microorganisms with food. The ingested microorganisms multiply in the gut and can cause diseases like diarrhoea, typhoid fever and cholera; intestinal parasites can cause diseases such as amoebiasis and taeniasis (tapeworm disease); and zoonotic foodborne diseases (i.e. those that are transmitted to humans from other animals), e.g. anthrax and bovine tuberculosis.

There are many different kinds of foodborne diseases and they may require different treatments, depending on the symptoms they cause. Illnesses that cause acute watery diarrhoea or persistent vomiting lead to dehydration if the person loses more body fluids and salts (electrolytes) than they are able to replace. It is therefore important to rehydrate the person, ideally with oral rehydration salts (ORS), or if this is not available, a simple mixture of clean water with some sugar and salt is advised.

Electrolytes are salts in the body that conduct electricity; they are found in all cells, blood and other body fluids, and are essential for normal functioning.

9.3.3  A catalogue of foodborne diseases

Tables 9.1 and 9.2 in Appendix 9.1 (at the end of this study session) summarise the types of organism which cause food infections and food poisoning (respectively). The tables also show the types of food items that are the main risk factors for the associated foodborne diseases. You are not expected to memorise the details of these tables; use them as references that you can consult for information when you need it.


Look at Table 9.1. What do anthrax and tapeworm infection have in common?


Raw meat consumption from sick and dying animals (like ox, cow, sheep, goat, camel) is responsible for transmitting anthrax, and raw beef and pork are the source of tapeworm infection.

End of answer


Which foodborne infections in Table 9.1 are commonly associated with consumption of contaminated milk and dairy products?


Brucellosis, typhoid fever, non-typhoid salmonellosis, bovine tuberculosis, E.coli infection and listeriosis.

End of answer

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