Body Story

• Poultry

• Red meat

• Pork

• Eggs

• Dairy products

• Desserts

• Shellfish and fish

• Fruit and vegetables

• Canned foods

Your fridge may look innocent, but it could hold all manner of unpleasant things. Living on and in the food we eat there are a host of different types of bacteria — microscopic organisms that may be beneficial to humans but may equally cause them harm. According to the Food Standards Agency, there are an estimated 4.5 million cases of food poisoning every year. The most common causes are Salmonella and Campylobacter bacteria, which are together responsible for about 500,000 of these cases.

The foods most often guilty of causing food poisoning are poultry meat, red meat, eggs and desserts, according to the Communicable Disease Surveillance Centre. Shellfish, pork and dairy products are also capable of delivering some nasty surprises.

• Poultry
Chicken carry the strain of bacteria, Salmonella enteritidis, which is now the single most common cause of salmonella food poisoning in the United Kingdom. The carrier chickens have no apparent symptoms but a human who has consumed infected eggs or infected chicken meat will suffer stomach cramps, diarrheoa, nausea, and fever. The recent increase in S. enteritidis infections is thought to be a direct consequence of modern farming methods, in which hundreds of thousands of chickens are bred in close proximity, enabling the bacteria to infect large numbers of birds. The problem is compounded when chickens from a single farm are distributed throughout the country, rapidly dispersing the infection to millions of people.

Poultry meat can contain Campylobacter as well as Salmonella bacteria, and Campylobacter is now the most common bacterial cause of gastro-enteritis in England and Wales. Eating undercooked chicken, or food that has been in contact with raw chicken, can cause this disease. As with Salmonella, the symptoms of infection include stomach cramps, diarrhoea and fever. They can last up to a week.

• Red meat
Red meat is also a source of Salmonella and Campylobacter. In addition, Escheria coli O157 (E. coli) is found in the intestines of healthy cows. In the early 1980s this bacteria emerged as an important cause of foodborne disease. Although it is not as common as Salmonella, up to 19% of people infected with E. coli go on to develop complications, including a syndrome that is a leading cause of kidney failure in children. Between 2% and 10% of children who suffer such kidney failure die.

Scientists recommend avoiding undercooked beef, which is the primary source of E. coli bacteria in food. Beef should be cooked at temperatures of 74°C (165°F) or higher to avoid the risk of food poisoning.

• Pork
Pork may contain the same strains of bacteria that are found in red meat. In addition, Yersinia enterocolitica is found in pork. This strain of bacteria can cause gastro-enteritis and is more severe in children. Recovery is normally complete within one to two days, but sometimes symptoms are mistaken for those of appendicitis, which results in a number of unnecessary operations to remove healthy appendix organs. Y. enterocolitica can survive refrigeration temperatures, but it is inactivated at cooking temperatures of 65.5°C (150°F) or above.

• Eggs
Like poultry meat, eggs can be infected with Salmonella. Cracked and dirty eggs should not be used, and eating raw eggs or runny egg yolks should be avoided. Commercially prepared foods with raw eggs are safer than home-prepared ones because the commercial products contain pasteurised eggs, which have been heated to kill any Salmonella bacteria present. All eggs, and food containing eggs, should be refrigerated; and after contact with raw eggs, hands and cooking utensils should be thoroughly washed.

• Dairy products
Dairy products such as milk, yoghurt and soft cheeses can also be sources of disease-causing bacteria. Salmonella, Campylobacter and E. coli are all found in dairy products.

Listeria monocytogenes, a particularly adaptable type of bacteria causing food poisoning, can also be found in dairy products such as cottage cheese and ripening cheddar. Refrigeration temperatures are not sufficient to inhibit the growth of Listeria bacteria, which makes them difficult to control, although temperatures of 79.5°C (175°F) or higher will inactivate them. Disease caused by Listeria may be so mild that it goes unnoticed, though it can cause flu-like symptoms. People with low immunity, for example newborn babies or the elderly, are far more susceptible. In fact, although death is very rare in healthy adults, 30% of sufferers of Listeria food poisoning who have weakened immune systems die from the disease.

• Desserts
Dessert-related outbreaks of food poisoning are caused by sources of bacteria in the dish’s raw ingredients, such as eggs, fruit and milk, and also by contamination by food handlers who can cross-contaminate different foods, or contaminate food themselves through poor personal hygiene.

• Shellfish and fish
Vibrio bacteria are commonly associated with shellfish food poisoning. This is not as a result of contaminated water, however, as the bacteria exist naturally in the sea. Again, symptoms are diarrheoa, nausea, stomach cramps and vomiting, but in some people infection from Vibrio bacteria can cause death within two days. People who are more susceptible include cancer and diabetes sufferers and people with liver disease, stomach problems or immune disorders.

Normal cooking should kill the bacteria. Raw seafood is a risk, and in Japan, where many seafoods are eaten raw, this type of food poisoning is a major problem. If you eat raw oysters because you've been told they're an aphrodisiac, you might be better off sticking to soft lights and Barry White.

Contaminated water may cause shellfish food poisoning, although developing Salmonella from infected shellfish is very rare in the UK.

Other food poisoning outbreaks associated with shellfish are thought to arise from viruses rather than bacteria. These viruses are described as SRSVs (small round structured viruses) and cause similar symptoms to those caused by bacteria. Shellfish are often cultivated in estuaries and inlets that are also used for sewage disposal, from which shellfish, pick up and concentrate viruses. Even good cleaning will not kill these viruses. It is therefore sensible not to eat raw or partly cooked shellfish.

Disease caused by infected fish is less common: cooking fish until it flakes and loses its translucent appearance is normally enough to avoid the risk of food poisoning. Fish that is not fresh can smell and taste like ammonia. Although it is not dangerous, it is better not to eat fish that has a strong smell.

• Fruit and vegetables
Fruit and vegetables are susceptible to contamination with Salmonella, Campylobacter, Listeria and SRSVs, through the use of manure containing animal faeces and through contaminated water. Fruit and vegetables are not a common source of foodborne disease, although restrictions to the disposal of sewage in the sea may lead to increased contamination of agricultural land, with an increase in the incidence of food poisoning associated with fruit and vegetables.

• Canned foods
Botulism caused by Clostridium botulinum bacteria is a rare but life-threatening disease which causes death in 30% of all cases. The bacteria are widely spread in our environment but become dangerous in certain conditions when they produce a toxin that is one of the most lethal known to humans. The toxin causes paralysis, and victims commonly suffocate as a result of paralysis of the lungs.

The conditions necessary for the production of this toxin are an oxygen-free environment and low acidity. Improperly canned low-acid foods, such as green beans, mushrooms, spinach, olives, beef and fish can provide this environment. Bulging cans, or canned food with a poor smell, should be avoided, though there may be no apparent signs of infection. The toxin can be destroyed by boiling food for 10 minutes.

Salmonella attack | Food scares | Dangerous foods

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