What is food poisoning?

Food poisoning is defined as any disease of an infectious or toxic nature caused by the consumption of food or drink. The term is most often used to describe the illness, usually diarrhoea and/or vomiting caused by bacteria, viruses or parasites. Very occasionally poisonings from chemicals may be the cause.

How common is food poisoning?

In the United Kingdom about 2 million people a year suffer from an attack of diarrhoea and/or vomiting due to food poisoning. Most do not consult their doctor and the cause is not often found. Food borne microbes are isolated in only about 100,000 cases a year and although large outbreaks can occur, usually only one or two people are affected.

Which bacteria cause food poisoning?

The bacteria most commonly found (about 40,000 cases annually) are called Campylobacter. These may be present in unpasteurised milk or raw poultry. Birds pecking the tops of milk bottles may infect the milk on the doorstep but in most cases the contaminated food is not identified.

Salmonella is the next most commonly found group of bacteria (about 30,000 per annum). They may be present in raw meat, poultry and occasionally eggs. For the remainder, Staphylococcus Aureus, Clostridium Perfringens and Bacillus Cereus produce toxins or poisons in food which may result in severe vomiting. C. Perfringens is usually associated with meat and B. Cereus with rice.

Some variants of normal intestinal bacteria are a cause of food poisoning. A particularly severe type is caused by E. Coli 0157. It is present in some cattle and may contaminate raw meat. It can cause bloody diarrhoea and kidney failure, particularly in the elderly, but is only rarely a cause of food poisoning.

What are the symptoms of food poisoning?

Vomiting and/or diarrhoea are the most common symptoms. Fever, abdominal pain or blood in the stools may occur. The illness is usually short lived but can be very serious or even life threatening, particularly at the extremes of life. Full recovery may take between a few hours to several weeks depending upon the fitness of the patient and the type of infection.

How quickly does it happen?

Some types of food poisoning can produce symptoms within a few hours of the contaminated food being eaten, whilst others may not occur for some days. S. Aureus or B. Cereus will typically cause illness between 2-12 hours after the meal, whilst symptoms of Salmonella or Clostridium Perfringens usually develop between 12-24 hours afterwards. Infections with Campylobacters are slow to produce symptoms and illness may occur up to a week or more after the infected food has been eaten.

What can be done to avoid food poisoning?

It is not necessary to avoid those foods commonly implicated in food poisoning, since Salmonella, Campylobacter and E.Coli 0157 are killed in foods, provided they are adequately cooked. Important points to remember are detailed below.

	Prevent the growth of bacteria by ensuring that all food stored in the refrigerator is covered and adequately chilled (ideally around 5° centigrade) and take care that chilled or frozen foods are not allowed to warm up in the hot boot of a car on the way home from the shops.
	Always wash your hands after visiting the lavatory.
	Take care to ensure thorough cooking and re-heating of all meat, especially poultry. Make sure that deep frozen food is thawed before cooking. This is especially important when using a microwave oven. Burgers should be cooked until there are no pink bits left and the juices run clear. Everyone should be aware of the small risk associated with foods containing uncooked eggs such as mayonnaise and certain puddings. Ensure that red kidney beans are always cooked for the recommended time to remove the toxin that is present in the raw beans.
	Wash your hands after handling raw meat or eggs, particularly before handling other foods.
	Do not re-use utensils with which you have prepared raw eggs or meat without first washing them with hot water and detergent. Do not allow juices from raw meat to come into contact with other foods.
	Avoid eating raw eggs or uncooked foods made from them.
	Vulnerable people e.g. the elderly, the sick, babies and pregnant women should eat eggs only which have been cooked until they are hard (both yoke and white).
	Wash salads thoroughly before eating.
	Do not drink any type of unpasteurised milk.

Treatment

Most food borne infections resolve without medical attention. Depending on the type of bacterial infection antibiotics may be prescribed in some cases. Before doing this, the doctor will usually require a stool specimen for analysis, in order to discover which particular bacterium is responsible.

Dehydration caused by diarrhoea and vomiting should be treated immediately with oral rehydration solutions available over the counter at chemists. If these preparations are not available, you can make your own using a generous pinch of salt (1.5gram) and a teaspoon of sugar stirred into a glass of fruit juice or water (250ml).

This is particularly important for infants and young children. If the illness lasts more than a few days or there is blood in the stools, medical advice should be sought urgently.

The need for research

Much is known about the organisms that cause food poisoning. Building on this knowledge, doctors and scientists are currently researching ways to diagnose infections more rapidly and to develop vaccines against them. Greater understanding of the mechanisms involved in the transmission of food borne infective disease is very important in improving standards of public health.