Friday July 19 2013
Food poisoning is often caused by poorly stored or prepared food
Can fruit and vegetables be dangerous? The Mail Online seems to think so. A story published on the website warns that: “Getting your five a day is responsible for half of all food poisoning cases.”
The story comes from a decade-long US study of the sources of foodborne illnesses in the US. It estimates that nearly half of all foodborne illnesses were caused by fruit, nuts and vegetables, particularly green leafy vegetables. Meat and poultry accounted for around one in five cases.
The study highlights the important fact that any foodstuff, if it is improperly prepared or stored, can cause food poisoning.
The germs responsible for these illnesses attributed to leafy vegetables commonly include E. coli and the winter vomiting bug, norovirus. These highly contagious germs are often spread “hand-to-mouth” (usually through not washing hands properly after going to the toilet).
However, these results do not mean that fruit and vegetables are bad for you, only that it is crucial to have high standards of personal and food hygiene.
There are rules covering the hygiene requirements of environments and personnel involved in the preparation and handling of food in the UK.
Meanwhile, in the home there are many ways you can help to stay safe, including washing your hands before handling and eating food, thoroughly washing raw fruit, vegetables and salads before eating, taking care over the storage of food and ensuring that meat for your weekend barbecue is thoroughly cooked.
Where did the story come from?
The study was carried out by researchers from the US Centers for Disease Control and Prevention, which is funded by the US government. The study was published in the peer-reviewed open-access journal Emerging Infectious Diseases.
The Mail Online’s headline appears to be confusing and perversely scaremongering, as it implies that eating five portions of fruit and vegetables increases your risk of food poisoning – a claim that is not supported by the study. A more useful headline would have explained the cause of the problem – poorly prepared, handled or stored fruit and vegetables can lead to food poisoning.
This frankly silly type of headline writing is a shame as the actual article is very well written and should be congratulated for highlighting the often ignored issue of ‘fruit and veg’ associated food poisoning.
What kind of research was this?
In this study, researchers aimed to calculate which specific foods and food groups were responsible for food poisoning outbreaks reported in the US between 1998 and 2008. They used this information to estimate the foods chiefly responsible for foodborne illness.
The authors point out that, despite advances in food safety, more than 9 million people suffer food poisoning in the US each year.
They say that one challenge in preventing foodborne illness is to decide where to prioritise food safety efforts, when a number of different foods may be involved (such as meat, fish or salad).
Attributing all illnesses to specific foods is challenging because most food pathogens are transmitted through a variety of foods and linking an illness to a particular food is rarely possible except during an outbreak.
Food poisoning can be caused by a range of different pathogens. These include bacteria (such as salmonella and E. coli), viruses (such as norovirus, known as the ‘winter vomiting’ bug), chemicals, and parasites (such as cryptosporidium). In the UK, most cases of food poisoning are caused by bacteria or viruses.
Most cases of food poisoning are not serious, although they are usually unpleasant. Complications can occur in more vulnerable people, such as older people, and they may require admission to hospital, for example due to dehydration.
It is estimated that in the UK, food poisoning is to blame for 20,000 hospitalisations and 500 deaths every year.
What did the research involve?
For their study, the researchers used data on food poisoning outbreaks in the US reported to the US Centers for Disease Control and Prevention (CDC) from state and local health departments, through an established surveillance system.
These reports include the number of people taken ill, the suspected or confirmed cause of the outbreak (the pathogen or ‘bug’), the implicated food “vehicle” (the meal that caused the poisoning) and the identity of contaminated ingredients in that food.
They say that during 1998-2008, a total of 13,352 foodborne disease outbreaks, causing 271,974 illnesses, were reported in the US. Of these, they looked at 4,887 (37%) which were attributed to a particular food “vehicle” (source) and a single cause. They excluded 298 of these outbreaks because not enough information about the food “vehicle” was provided to categorise ingredients.
They obtained data on the estimated number of illnesses, hospitalisations and deaths for each outbreak.
The researchers then created 17 mutually exclusive food groups or “commodities”:
- three for aquatic animals (fish, crustaceans and molluscs)
- six for land animals (dairy, eggs, beef, game, pork and poultry)
- eight for plants (grains and beans, oils and sugars, fruits and nuts, fungi, and leafy, root and vine-stalk vegetables)
They also divided foods into those that were “simple” (containing ingredients from one group or commodity only (such as apple juice or fruit salad) and “complex” (containing ingredients from more than one commodity, such as apple pie (made from fruit, flour, sugar and dairy).
They then calculated the proportion of outbreak-associated illnesses transmitted by each food commodity, taking account of whether foods involved in the outbreaks were complex or simple. They then applied the percentages they derived from the data to the 9.6 million estimated annual illnesses in the US caused by food poisoning. They provided a range of estimates, using the most probable estimates in their results.
What were the basic results?
The researchers included 4,589 food poisoning outbreaks and 120,321 cases of food poisoning in their study. They found that norovirus (the most common cause of diarrhoea and vomiting in the UK and elsewhere) caused the most outbreaks (1,419) and illnesses (41,257) in the US during the period analysed.
Causes of foodborne illness
- plant commodities – fruits, nuts and vegetables – accounted for 46% of foodborne illnesses
- meat and poultry accounted for 22% of illnesses
- among all 17 commodities, more illnesses were attributable to leafy vegetables (2.2 million or 22%) than any other commodity
- after leafy vegetables, commodities linked to the most illnesses were dairy (1.3 million 14%), fruits and nuts (1.1 million, 12%), and poultry (900,000, 10%)
Hospitalisations for food poisoning
- 46% (26,000) of annual hospitalisations were attributed to meat and dairy (land animals)
- 41% (24,000) were attributed to plant foods
- 6% (3,000) were attributed to fish and other seafood (aquatic animals)
- dairy foods accounted for the most hospitalisations, followed by leafy vegetables, poultry and vine stalk vegetables
Deaths from food poisoning
- an estimated 43% (629) deaths each year were attributed to meat (land animals), 363 (25%) to plant foods and 94 (6%) to fish and other seafood (aquatic animals)
- poultry accounted for the most deaths (19%) followed by dairy (10%), vine stalk vegetables (7%), fruit-nuts (6%) and leafy vegetables (6%)
They also say that plant foods accounted for 66% of viral illness, 32% of bacterial, 25% of chemical and 30% of parasitic illness.
How did the researchers interpret the results?
The researchers point out that more illnesses were attributed to leafy vegetables (22%) than to any other commodity. In addition, illnesses associated with leafy vegetables were the second most frequent cause of hospitalisations (14%) and the fifth most frequent cause of death (6%). Efforts are particularly needed to prevent contamination of plant foods and poultry, they argue.
This large study of the possible sources of food poisoning in the US over a ten year period comes from a reputable source. However, as the authors point out, it can only give estimates as to the sources of food poisoning and it is also based on data before and up to 2008.
Since that time, patterns of food poisoning and the agents which cause it, may have changed. Also, its calculations are based on only a third of all food poisoning outbreaks in the US during the ten years covered.
It should also be noted that the findings may not apply to food poisoning trends in the UK.
Nevertheless, the findings of the study are of concern and a timely reminder of the crucial importance of food hygiene. The germs responsible for these illnesses attributed to leafy vegetables mostly include those highly contagious germs that are most often spread from the hand to the mouth, especially if you haven’t washed your hands properly after going to the toilet.
While this study did not explore the causes of these outbreaks, the vegetables would have most likely been contaminated by the hands of people carrying these bacteria at any stage along the line of production, processing or preparation.
There are high standards covering the hygiene requirements of environments and personnel involved in the preparation and handling of food in the UK. And ensuring food is safe to eat is a legal responsibility of both those involved in food production and processing. However, you should be wary of being complacent about food hygiene.
You can reduce your risk by:
- always washing your hands before handling and eating food
- thoroughly washing raw fruit, vegetables and salads before eating
- ensuring produce such as fresh produce doesn’t come into contact with raw meat
- ensuring that meat is thoroughly cooked
- when reheating items ensure that they are thoroughly heated through
- ensuring that meats, fish, dairy products and prepared meals are refrigerated, and not left standing in the room or outside (in hot temperatures, the time after which such food will become unsafe to eat will be less)
- observing use-by dates
Read more about preventing food poisoning.
Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on Twitter.