Large numbers of people are affected by food-borne diseases each year. In the US the Centers for Disease Control and Prevention (CDC) estimates that there are 76 million illnesses each year from both known and unknown causes. In the UK the Food Standards Agency estimates there are about one million cases a year. The severity of food-borne infections can range from mild discomfort to life-threatening illness.
The vast majority of these result from preventable causes in the food supply chain or during food preparation and storage. By following the basic advice below you can greatly reduce your chances of illness. This article covers:
- How do you catch food poisoning?
- Four common microorganisms causing food poisoning
- Symptoms of food poisoning
- Preventing food poisoning
- How to defrost frozen poultry
1. How do you catch food poisoning?
The microorganisms that cause food poisoning either are present in the food when you buy it or are put in the food by ‘cross contamination’ where food is prepared, in the factory, supermarket, restaurant or by you in your home. There are five categories of causes of food poisoning, according to the US CDC:
- Food from unsafe sources
- Poor personal hygiene
- Inadequate cooking
- Improper holding/time and temperature
- Contaminated equipment/protection from contamination
Bacteria, viruses or parasites are often present in food such as raw meat in low numbers that do not cause a risk if the food is handled and cooked properly. They can become more dangerous, however, if allowed to multiply or contaminate other food through poor handling and storage practices at any stage until you eat it.
Causes of food contamination in the home or restaurants include:
- Keeping food past its use-by date
- Storing food that should be chilled (eg raw meat, cooked meats, cheese) at temperatures above 5°C
- Not cooking food properly
- Cross-contamination caused by unintentionally spreading bacteria/viruses between foods, especially raw poultry, and surfaces, including work surfaces, chopping boards, utensils, equipment and taps
- Poor personal hygiene by people who are ill, especially not washing hands properly
- People who are ill touching food or surfaces where food will be placed, or coughing and sneezing nearby
- Using contaminated water or other liquids
- Touching contaminated objects then food or surfaces where food is placed
- Touching pets then food or kitchen utensils
- A wide range of pests can contaminate food in the home, restaurants, and hotels.
2. Four common microorganisms causing food poisoning
There are over 200 microorganisms known to cause food poisoning. Four of the most common in many developed and developing countries are described below:
- E. coli
There are many strains of Salmonella bacteria, called serotypes, but most infections are caused by just a few of them. Children under five, elderly people and those with weakened immune systems are more vulnerable to severe infections.
Salmonella is mainly found in raw meat and eggs, so illness is usually caused by eating raw or undercooked food. Most people develop the illness between 12-72 hours after infection and it usually clears on its own in 4-7 days.
Campylobacter bacteria are one of the most common causes of food poisoning worldwide. There are over 30 species of Campylobacter but one species, Campylobacter jejuni, causes most cases of campylobacteriosis. It is common in the gut of birds, which do not become ill, and grows best at 37–42°C. Cattle and pets can also carry the bacteria in their faeces.
Campylobacter gets into the food chain mainly through raw or undercooked poultry and water or food products contaminated with animal faeces, such as unpasteurised milk.
A high percentage of chicken in grocery stores is contaminated with Campylobacter. The UK Food Standards Agency in 2015 reported that 73% of fresh whole chickens in supermarkets carried the bacteria.
However, the bacteria does not survive well outside its natural environment and is easily killed by cooking food properly. Infection can be avoided by following the basic food hygiene practices described below.
Escherichia coli (E. coli) is a diverse group of bacteria that occur naturally in the intestines of most animals and are mostly harmless. Some strains can cause serious illness, the most common of which is called Shiga toxin-producing E. coli, or STEC for short. Young children and the elderly are the most likely to get a severe infection. This can cause high fever, diarrhoea with blood and vomiting.
STEC is mainly caught via cattle, through products such as minced/ ground beef, unpasteurised milk and also water contaminated with faeces.
People who have the infection can spread E. coli through poor hygiene, or in the case of babies and young children, their parents or carers can easily pick up spread the bacteria. The incubation period is 1-10 days and symptoms last from several days to weeks, during which the infected person can shed the bacteria.
Norovirus is highly contagious and one of the most common causes of diarrhoea and vomiting. It is the most common cause of diarrhoea worldwide, causing over 200,000 deaths in developing countries each year. It is the leading cause of food-borne disease in the US, according to the US CDC. In the US each year Norovirus causes or leads to:
- 19–21 million cases of acute gastroenteritis
- 1.7–1.9 million hospital outpatient visits
- 400,000 emergency department visits
- 56–71,000 hospitalisations
- 570–800 deaths
The number of cases peak in winter and is mainly first caught from leafy vegetables, fresh fruit and shellfish. The virus is tolerant of high temperatures (140°F/ 60°C) therefore foods that are lightly cooked, such as shellfish, can still cause food poisoning after cooking.
Once caught by one person, it can spread rapidly to others in the same household, but especially in institutions such as hospitals and care homes where visitors can introduce it to vulnerable patients and residents. The incubation period is 24-48 hours and it usually lasts 1-2 days.
3. Symptoms of food poisoning
Although, as mentioned earlier, many different microbes can cause food poisoning, the symptoms are usually similar. These include:
- Feeling sick
- High temperature
- Stomach or abdominal cramps/ pain
- Aching muscles
- Loss of appetite
Most cases of food poisoning clear up on their own in a few days. The UK NHS advice is that for mild cases it is better not to go to a doctor, to prevent spreading the disease. But if the illness is more severe or you have underlying conditions you should seek medical advice.
4. Preventing food poisoning
The UK Food Standards Agency recommends following ‘the 4 Cs’ of food hygiene:
- Cross-contamination prevention
Wash your hands
The most important measure you can take is to wash your hands with soap and warm water at critical times:
- Before preparing food, especially food that will be eaten raw or without further cooking
- After handling raw food, especially raw poultry and food with soil on it
- After going to the toilet
- After touching pets, waste bins and other obvious sources of contamination such as sneezing into your hands
Initial’s hand washing monitoring system helps businesses reduce the risk of food contamination by encouraging staff to wash their hands properly.
How you wash your hands makes a big difference to the number of germs removed. You should wash your hands with soap and water for 20 seconds to clean and rinse them properly. The rinsing also helps to remove more germs from your hands.
Clean work surfaces, chopping boards, equipment and cooking areas before and after preparing food. The average chopping board has twice as much faecal bacteria as a toilet seat, according to the UK NHS. Use separate boards and knives for raw meats, vegetables and other foods to prevent cross contamination between raw and ready to eat foods.
Clean food handling areas
Clean floors when there are spills and clean them regularly to prevent dirt and grease build up. Store waste, such as discarded food containers, plastic bags, bottles and waste food, in suitable containers. Remove waste regularly to prevent it decaying or attracting food pests such as rats, mice, cockroaches and flies that are a food safety hazard.
Clean the cleaning materials
Cloths, sponges and mops can be ideal breeding grounds for bacteria, so clean them well after use and don’t let food material, including from dishwashing water, accumulate in them.
Restaurants and kitchens in schools, care homes etc, should use disposable cloths and discard them after each use.
Safe cooking temperature
The most important foods to cook thoroughly are raw meats and seafoods. These have to reach a critical temperature to kill off any dangerous bacteria and other microorganisms.
Poultry, sausages and burgers have to be cooked properly throughout to be safe. Check that all the meat is cooked by inserting a knife into the thickest part and looking deep down in the cut to see if there is still red meat or blood.
Checking the internal temperature of chicken during cooking
You can also use a cooking thermometer to see if the insides have reached the critical temperature. According to US FoodSafety.gov guidelines meat should reach these temperatures internally:
- Poultry: 165°F/ 74°C
- Stuffing: 165°F/ 74°C
- Burgers, sausages: 160°C / 71°F
- Beef, lamb, pork, ham: 145°C / 63°F
Cover leftovers and store them in the fridge as soon as they are cool. There is a balance between leaving food out for too long while it is cooling down and putting it in the fridge where it can increase the temperature of other foods.
General guidelines recommend keeping cooked food in a fridge for at most two days. Many home fridges are too warm to store food for long, so if you don’t have a thermometer built in get one to check that the temperature is below 5°C.
If you reheat cooked food from the fridge make sure it is steaming hot throughout to kill any microorganisms that have multiplied during storage.
Cross contamination of food occurs when bacteria or other microorganisms are transferred from infected foods or surfaces to other foods. This can occur by contact with contaminated hands, surfaces, tools and equipment, or contaminated dripping liquids.
Follow these eight practices to prevent cross-contamination:
- Wash your hands before preparing food
- Wash your hands after touching raw foods so you don’t cross-contaminate other foods and surfaces and do not transfer germs from your hands to your mouth
- Store raw food and fresh foods separately so they do not touch
- Store raw meat and poultry so that it cannot touch or drip blood onto other foods. Put it in a sealed container or bag, on the bottom shelf of the fridge. At the very least, place it in a suitable container to collect raw blood. This is important when frosting as blood tends to leak out of the meat
- Use different utensils and chopping boards for preparing raw meat, fruit and vegetables and ready-to-eat foods. It is a good idea to follow the practice of the professionals and have different coloured boards to help you remember which one to use for each food type
- Clean surfaces and chopping boards thoroughly before and after preparing food
- Do not wash raw poultry or meat as this can splash bacteria such as Campylobacter around the sink and other parts of the kitchen and everything your wet hands drip onto, such as the taps. The UK Food Standards Agency launched a campaign in 2014 to stop the widespread practice of washing poultry to prevent Campylobacter food poisoning — the most common cause of food poisoning across Europe. Some supermarkets have also started putting warning messages on packets to prevent food poisoning
- Regularly change or clean sponges, cloths, brushes and towels used to clean, wipe and dry in the kitchen. Used them carefully to prevent cross-contamination. It is easy to handle raw meat and poultry then wipe surfaces or your hands before washing them. Also, you might pick up the same contaminated sponge or cloth later when your hands are clean. Wet sponges and cloths are ideal breeding grounds for bacteria, especially when laden with food particles
5. How to defrost frozen poultry
Undercooked poultry is one of the worse food hazards because the disease-causing microorganisms are so common in the birds. When poultry such as chicken and turkey is frozen you have to be especially careful to make sure the meat is both thawed completely before cooking and it is cooked thoroughly to kill all dangerous microorganisms.
A chicken can be defrosted overnight, but it can take several days for a large bird such as a turkey. The time depends on the weight of the bird and the temperature of the surroundings — the fridge or room where you store it:
- In a fridge at 4°C/ 39°F: 10-12 hours per kg. For an 8kg bird this means 4 days!
- In a cool room (15°C): 7 hours per kg. For an 8kg bird this is 2-3 days
- At room temperature (20°C): 2 hours per kg. This still takes an 8kg turkey 16 hours to defrost and at this temperature. It then has to be cooked immediately to prevent the meat going off
While the meat is defrosting it can drip blood so make sure the packaging is well sealed or it is placed on a suitable tray and will not touch or drip onto other foods or surfaces.