Sep 26 2005
Madeleine Brindley, Western Mail
Last week was dominated by the growing E.coli O157 outbreak which hit schoolchildren across South Wales. As food-borne illnesses continue to affect millions every year, Health Editor Madeleine Brindley and the Food Standards Agency Wales present an instant guide to food poisoning
EVERY year it is estimated that one in 10 people will suffer from a bout of food poisoning as a result of eating food contaminated with bacteria.
At its most serious, food poisoning can lead to severe illnesses and even kill.
Bacteria and germs in food are very hard to detect because they do not affect either the taste, appearance or smell of food.
The most serious types of food poisoning are caused by bacteria – the more bacteria present, the more likely you are to become ill, although as little as 100 E.coli O157 organisms in food are enough to cause a serious illness.
Bacteria multiply fast when they have a ready supply of moisture, food, warmth and time. The presence or absence of oxygen, salt, sugar and the acidity of the surroundings are also important factors in their growth.
In the right conditions one bacterium can multiply to more than four million in just eight hours.
Bacteria multiply best between 5C and 63C but are killed at temperatures of 70C. At temperatures below 5C, most bacteria multiply very slowly, if at all.
At very low temperatures some bacteria will die, but many survive and can start to multiply again if warm conditions return, making the proper cooking and chilling of food essential to reduce the risk of food poisoning.
Germs and bacteria can get into our food at any point in the food chain – from the time when an animal or food is in the field to the moment food is put on to the table to eat.
Bacteria can also be spread to other foods by unwashed hands, or kitchen utensils.
The symptoms of food poisoning can last for days and include abdominal pains, diarrhoea, vomiting, nausea and fever.
Campylobacter is the most common identified cause of food-borne disease.
It has been found mainly in poultry, red meat, unpasteurised milk and untreated water.
Although it doesn’t grow in food it spreads easily, so only a few bacteria in a piece of undercooked chicken could cause illness.
Infections do not usually cause vomiting, but diarrhoea can be severe and bloody with abdominal cramps.
Clostridium perfringens is found in low numbers in many foods, particularly meat and poultry and their products.
It is also found in the soil, the intestines of humans and animals, in sewage and in animal manures.
Infection normally causes diarrhoea and severe abdominal pain. It may occasionally cause nausea but it rarely causes vomiting or fever.
Unlike many other types of bacteria that cause food-borne diseases, Clostridium perfringens isn’t completely destroyed by ordinary cooking. This is because it produces heat-resistant spores.
The bacteria are killed at cooking temperatures, but the heat-resistant spores they produce are able to survive and may actually be stimulated to germinate by the heat.
If the food is not eaten at once but is allowed to cool slowly, the bacteria produced when the spores germinate multiply rapidly.
Unless the food is reheated so that it is piping hot – at least to 60 C and preferably to 75 C – the bacteria will survive.
Foods most likely to be associated with Clostridium perfringens food poisoning are those that are cooked slowly in large quantities and left to stand for a long time at room temperature.
Salmonella is the second most common cause of food poisoning after campylobacter.
It has been found in unpasteurised milk, eggs and raw egg products, meat and poultry and it can survive if food is not cooked properly.
Salmonella can also grow in food – if a small number of bacteria are present in a food, they will multiply unless it is chilled.
People infected with salmonella should be particularly careful with personal hygiene because they could infect another person who comes into direct contact with them.
Listeria monocytogenes is present all around us in the environment. It has also been found in low numbers in many foods.
In certain foods, such as soft mould-ripened cheeses and pate, it may be present in higher numbers.
Eating foods containing high levels of Listeria monocytogenes is generally the cause of illness.
It usually causes illness in vulnerable groups such as pregnant women, babies, the elderly and people with reduced immunity. Among these groups, the illness is often severe and life-threatening.
Pregnant women should avoid soft mould-ripened cheese, such as Camenbert and Brie, blue cheese, and all types of pate.
Most strains of E.coli are harmless, but those that produce verocytotoxin – called verocytotoxin-producing E.coli, or VTEC – can cause severe illness. In the UK, the most common type is E.coli O157.
E.coli O157 has been transmitted most commonly through undercooked minced beef and milk that is unpasteurised, inadequately pasteurised or contaminated after pasteurisation.
It is also possible to become infected by direct contact with infected animals or people, and by contact with land contaminated with animal faeces.
Common symptoms include diarrhoea and abdominal cramps. The illness can also have very serious complications, including kidney failure, severe anaemia and neurological problems.
Sometimes E.coli O157 infections can lead to death, as in the 1996 Scottish outbreak which caused 20 deaths.