Microorganisms are everywhere and are usually harmless. However, some can make us very sick. Food poisoning is mainly caused by bacteria, viruses and, less commonly, by parasites. These organisms generally come from infected food handlers, animal faeces and soil.
Bacteria are microscopic organisms. There are many different types; some we want in our foods, others cause food to spoil, and some can make us sick.
We use helpful bacteria to make foods such as yoghurt, most cheeses and salami-type meats because they promote fermentation.
Other types of bacteria spoil food, making it smell and taste bad, but these types, such as Pseudomonas, which causes spoilage in eggs, milk, cheese, meat and fish, are usually harmless.
Bacteria that cause food poisoning are found mainly in animal faeces and in soil. Humans can have these bacteria in their faeces, mouth, nose and ears, and in infected sores.
Food poisoning bacteria do not change the smell, taste or appearance of the food. They include: Salmonella, Campylobacter jejuni, Staphylococcus aureus, certain strains of E. coli and Listeria monocytogenes.
Often food poisoning bacteria need to grow to large numbers in food to cause illness, which is why it is important to keep certain foods refrigerated or very hot. Others don’t need to grow to cause illness, which is why we need to protect food from contamination.
Viruses are even smaller than bacteria. When in foods, even in tiny amounts, they can make us sick. Foodborne viruses include hepatitis A and noroviruses.
Viruses are excreted in large numbers in the faeces – and for norovirus in particular, the vomit of infected people. If food handlers are infected they can contaminate food.
Food can also be contaminated if it is washed or grown in water containing human sewage. Oysters are particularly susceptible if grown in sewage-affected water.
Parasites such as worms live inside people and animals. They are excreted in faeces and can contaminate meat during slaughter and fruit and vegetables grown in soil fertilised with manure. Examples include Cryptosporidium parvum and Giardia lamblia.
Preventing food poisoning
There are simple things you can do to prevent food poisoning; including washing and drying your hands thoroughly before preparing food and after handling raw meat; not preparing raw meat and vegetables/fruits on the same surface; not preparing foods for other people when you are sick, washing foods that aren’t going to be cooked (e.g. salad vegetables) and keeping certain foods very cold or very hot.
In Australia, all food businesses must comply with Food Safety Standards:
What happens when things go wrong?
Food businesses have systems in place to prevent contamination of food. But even with the best systems, contamination with bacteria or viruses sometimes happens. This is why Australia has a well-established system for recalling food. Recalls are coordinated by FSANZ in consultation with the food business recalling the food and the states and territories.
If a food business discovers it has sold unsafe food, it must immediately stop further sales and recall the food. It must let consumers know, through an advertisement in a paper, a media release or shop front sign, that the food may be unsafe and should be returned to the seller.
After a recall, a food business will determine what went wrong and put in place new procedures to reduce the chance of it happening again.
Food recall system
Food Safety Information Council
Agents of foodborne illness