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International Scientific Forum on Home Hygiene

Background Information on Foodborne
Disease and the home

What is food poisoning?
Any disease of an infectious or toxic nature caused by or thought to be caused by the consumption of contaminated food or water.
What are the main pathogens that cause foodborne outbreaks?
The main microbial causes of food poisoning are bacteria (e.g. Salmonella, Campylobacter, Escherichia coli  O157, Clostridium, Staphylococcus aureus and Bacillus cereus) and viruses (e.g. Norovirus).
Campylobacter, Salmonella, Clostridium perfringens, verocytotoxin producing Escherichia coli (VTEC), Norovirus and Listeria monocytogenes are estimated to account for 85% of foodborne disease in England and Wales.
How does food and water become contaminated?

  • Foodborne pathogens frequently originate from the gastrointestinal tract of the animals from whom the meat is produced.  In some cases the animal is perfectly healthy e.g. cows who carry E. coli 0157 are themselves “healthy”. There are many opportunities for meat or poultry to become contaminated as it is slaughtered and prepared for sale.
  • Animals can also transmit food borne pathogens to humans via their produce e.g. milk, eggs
  • Therefore, raw foods of animal origin as purchased for consumption in the home are the most likely foods to be contaminated, i.e. raw meat and poultry, raw eggs, unpasteurized milk, and raw shellfish.
  • Outbreaks can also occur where vegetables or other farm produce becomes contaminated e.g. from contaminated water or raw sewage.

During food processing (either during production or in the home), intestinal pathogens can also be introduced from infected people who handle the food, or by cross contamination from some other raw foods.  The latter occurs either by direct or indirect cross-contamination from contaminated raw food such as meat, poultry and eggs to other foods e.g. cooked meats or salads to be eaten without further cooking:

  • Up to 25% of chickens sold through retail outlets in the UK are contaminated with Salmonella and up to 83% contaminated with Campylobacter. Similar or even higher figures are reported from other countries worldwide.
  • A UK study showed that 6% of the outside of retail poultry packaging was contaminated with Campylobacter and/or Salmonella.
  • 0.4%-0.8% of meat products purchased from UK butchers were positive for E. coli O157.

Examples of Number of Reported Food Poisoning Cases

  • England and Wales: >72,000 cases in 2002
  • Scotland: 7682 cases in 2002

Although the number of cases recorded is in the thousands, the true burden of food poisoning is likely to be millions of cases per year, as most cases go unreported.
England & Wales: According to the UK Food Standards Agency (FSA), up to half of the annual 9.4 million cases of infectious intestinal disease (IID) are food poisoning. This equates to up to 4.7 million cases per year.
UK: In a 2003 FSA survey, [MSOffice1] 16% of respondents said they had suffered food poisoning in last 12 months. This equates to up to 7.6 million cases per year.
US: Foodborne illness is estimated to cause 76 million illnesses, 500,000 hospital admissions, and 9000 deaths each year.
New Zealand: Foodborne illness estimated to cause 119,000 cases, 19000 GP visits, 400 hospital admissions, 22 cases of long term illness and 2 deaths per year. 
What proportion of foodborne infection occurs in the home?
In 2003, the World Health Organisation reported that as much as 40% of all foodborne infections are a result of food eaten within the home.
How does food poisoning occur in the home?
Of foodborne IID outbreaks in the home, UK data suggests that:

  • 39% are due to inappropriate storage of food
  • 31% are due to inadequate cooking
  • 20% are due to cross-contamination

The purpose of cooking food is to reduce the numbers of bacteria or viruses to a level insufficient to cause disease.  Both home-cooked foods and purchased cold foods such as cold ham, etc. should contain only small numbers of human pathogens that are insufficient to cause disease.  However, if left in warm or ambient and moist conditions overnight organisms can multiply and the food can become highly contaminated by the next day.

  • After heating, food must spend the minimum amount of time between 30ºC–45ºC.
  • If not eaten immediately, food must be cooled immediately to prevent the potential growth of bacteria.
  • Freezing prevents bacteria from growing and refrigeration will delay it.
  • Neither freezing nor refrigeration will inactivate bacteria, which means that on transferring these foods to room temperature they may become heavily contaminated again if left at warm temperatures.

Cross-contamination or contamination from an infected food handler, indicative of poor hygiene standards is thought to be responsible for about 20% of outbreaks in the home.  This can involve either direct or indirect cross-contamination. An example of direct cross-contamination is where an infected person directly contacts the food.  Indirect cross contamination is where the transfer of micro-organisms is via another vector such as a knife or a dishcloth.
In the kitchen, micro-organisms can be transferred from one food to another food by using the same chopping board or knife to prepare both without washing the surface or knife in between.  A food that is fully cooked can become re-contaminated if it touches other contaminated raw foods or drips and spills from raw foods.
Cloths and sponges become contaminated when they are used to wipe up spills from food, and bacteria can multiply with time once on damp cloths and sponges. Afterwards the cloths and sponges serve as a vector for further spread of pathogens to the hands of the user, to the surfaces wiped and then to many articles throughout the kitchen.

  • A recent study has shown that during the preparation of a meal in a domestic kitchen using a contaminated chicken almost 1 in 5 (17%) of hands and hand and food contact surfaces become contaminated with Salmonella or Campylobacter.
  • In a US study of 23 patients infected with E. coli 0157, 80% of the cases were thought to have originated from consumption of hamburgers in the home and food preparers in those home were significantly less likely to report washing their hands or work surfaces. The transmission was believed to have occurred more often when the hands of food preparers were allowed to cross-contaminate other food and utensils.
  • An outbreak of Norovirus at a wedding reception affecting 50% of guests was due to cross-contamination of potatoes from a contaminated sink, into which the food handler has previously vomited.

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