Food-borne diseases

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Updated on 2024

Lesson 4: summary

Food-borne diseases

Microorganisms act as a source of infection or food hazard. But what are microorganisms? They are also called germs or microbes and are living beings so small that they are invisible to the human eye.

Let’s list them according to the harm they can cause:

  • Beneficial: they are used for food processing.
  • Disruptive: they «warn» us of their presence, since they change the odour, colour, flavour and normal texture of the food.
  • Patogens: These are the most dangerous because at first glance they do not change the food properties. They are mainly responsible for food-borne diseases.

What do they need to live?

  • Nutrients: food.
  • Water.
  • Heat.
  • Acidity: as acidity increases, they become less contaminated by bacteria..
  • Oxygen: some bacteria live on oxygen (most of them), but others also grow without it.
  • Time: the more time passes, the more they multiply and the greater the risk.

The most frequent symptoms are general discomfort, vomiting, diarrhea and abdominal pain. But the most dangerous ones can cause serious injuries and even death.

What food is more dangerous or likely to become contaminated?

Those that pose a MAJOR RISK are:

  • Minced meat.
  • Fresh fish, shellfish and molluscs.
  • Raw products.
  • Fowl and Poultry.
  • Egg-based dishes (use of raw eggs is prohibited).
  • Pastry or bakery goods (especially those containing cream).

Lesson 4: extended

Classification of food contaminants


Not all microorganisms are bad. Some of them are even used to make food (yoghurt, cheese, bread...).


These are responsible for the decay of the food. They "warn" us of their presence, since when they are in a food they cause it to change its normal smell, colour, flavour and texture. Therefore, normally, we will not use these foods when they have a "rare" appearance. If something smells bad or has a strange color, we will not eat it because it will be bad food.


These are the most dangerous, because at first glance they do not produce changes in the food. They are the usual producers of food-borne diseases.

Types of foodborne diseases

Food-borne illness is caused by eating contaminated food or drink. Most of these diseases are caused by bacteria, viruses and parasites. Most common foodborne diseases are viral and bacterial.


The most common diseases caused by bacteria are salmonella, campylobacteriosis, escherichia coli, listeria and vibrio cholerae. The manifestations of foodborne microbial diseases are usually gastrointestinal in nature, so the general symptoms of most microbial diseases are: abdominal cramps or pain, diarrhea (sometimes with bleeding), vomiting, and fever.

The presence of bacteria in food is not always visible, i.e. not whenever a food is contaminated by the presence of food bacteria, it will have changes in taste or smell or the appearance of the food will be altered. This is why it is so important to maintain proper prevention and hygiene in food handling.


Parasites are organisms that feed on the protective nutrients of other organisms known as hosts. These guests may be animals or human beings. Parasites can be present in both food and water and can cause disease. They are also transmitted from one host to another by the consumption of contaminated water or food or by contact with the mouth of any contaminated agent that has come into contact with the faeces of infected animals or persons.

The most common diseases transmitted by parasites are: trematodiasis, echinococcosis, toxoplasmosis, trichinosis, taeniasis, cysticercosis, giardiasis, crypto or cyclosporiasis.


The most common microbial disease caused by viruses is norovirus, the most common cause of acute gastroenteritis. It is a highly contagious virus that causes inflammation of the stomach and intestines, resulting in stomach pain, vomiting, nausea and diarrhea. Unlike bacteria, viruses are strict intracellular parasites and cannot replicate outside the host organism, their spread depends closely on it.

For this reason, viruses cannot be replicated in water or food, so during processing, transport or storage, viral food contamination will not increase and may actually decrease. Most viruses in food or water are resistant to disinfection and heat.

What do bacteria need to live?

They need basically the same things we do to live: water, food and something to take shelter in, to be "at ease" wherever they are. Specifically, they need:

  • Water: they need moisture or liquid. Therefore, if we remove the water from food (dehydrated, dried...), we will make it better preserved and not easily contaminated by microorganisms.
  • Nutrients: food.
  • Heat: they need to be at the right temperature to multiply. The most dangerous temperature is between 10ºC and 60ºC, as this is where they are best placed to divide. Only heat eliminates microorganisms, if we freeze food (colder than -18°C, i.e. -18°C, -19°C, -20°C...) it remains stable, "without moving" or multiplying, but if the food were to be put at a dangerous temperature, the bacteria would multiply. In refrigeration (between 0º and 5ºC), they multiply but very slowly. That is why it is important to keep the right cold temperatures for the food.
  • Time: if the conditions are right (they have water, food and heat), then the more time they have the more they multiply, and the greater the risk to the consumer. That is why it is important to keep food at the right temperature and protect it from different aggressions.
  • Acidity: by increasing the acidity, the food becomes less contaminated by bacteria. That is why some foods are added lemon, vinegar, etc...
  • Oxygen: bome bacteria live on oxygen ("breathe") but others grow without oxygen. Some of them are very dangerous such as Clostridium Botulinum which can develop inside cans.

Contamination factors

Bacteria, parasites and viruses appear, inhabit and reproduce in food when food safety conditions have not been adequate. Knowing the factors that favour the appearance of contaminants in food is key to preventing and detecting them, thus minimising the risks of contamination and contracting food-borne diseases.

  • Poor hygiene is one of the most common factors causing food contamination. To avoid this, as explained in Lesson 2 of this course, among others, it is essential that food handlers maintain good hygiene both in terms of food, storage and cooking facilities and in terms of the handler's own hygiene.
  • Cross-contamination is another factor affecting food contamination.
  • Unsanitary conditions: Improper slaughterhouse practices can lead to contamination, especially if livestock faecal matter is mixed with meat, as a small amount can contaminate a whole batch of meat. The same risk occurs in fruits and vegetables when they are fertilized with raw manure or when they are irrigated with contaminated water. Both meat and vegetables are associated with outbreaks of Escherichia coli.
  • Unsafe packaging: Homemade canning can pose a risk that can be prevented by sterilising empty jars, hot-packaging and using self-sealing lids.
  • Inadequate storage: bacteria multiply rapidly in a short time, so it is important not to leave food outside the refrigerator for more than two hours. It is recommended to eat or refrigerate raw foods such as creamy salads immediately.

Food prone to food-borne diseases

Any food can be susceptible to contamination, but it is true that there are some foods of higher risk, which by their nature, composition or form of culinary preparation make them perfect for bacteria to multiply in. Among these foods we find:

  • Egg-based dishes: mayonnaise, salad, etc... hence the use of raw eggs is prohibited, instead use pasteurized egg or egg products.
  • Minced meat: to make hamburgers, meatballs... the amount of food they have in contact with the air is much greater than a whole piece, not minced, so it is more likely to become contaminated.
  • Poultry and farm: chicken, hen, partridge...
  • Fresh fish, seafood and molluscs.
  • Raw products.
  • Pastry or bakery products: especially those containing cream.

More courses

More information

Food Standards Agency
Codex Alimentarius at FAO
European Food Safety Authority
WikiPedia - Food Safety


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