Report Compiled By Dr. Jill Warner Senior Lecturer in Allergy and Immunology University
of SouthHampton, UK. For the Healthy Flooring Network.

Everyone knows at least one person who suffers from some form of allergy. Up to a third of the population in developed countries is affected by allergic diseases such as asthma, eczema and hayfever. Today the prevalence of allergic diseases is extremely high, particularly in the English speaking westernised societies, and it has been clearly shown to have increased over the past few decades.

The UK has the highest prevalence of asthma symptoms in 13-14 year olds in the world, at 19.8%; the second highest prevalence of eczema; and the twelfth highest of rhinoconjunctivitis. The indoor environment has been cited as one of the possible reasons for this increase.

Indoor Allergens
The factors that are likely to have the most effect on disease management in the short term are those that, while suggested to be potentially useful in primary prevention, also address the problems of reducing symptoms in already sensitised individuals. Indoor allergens are one such area that might provide possible intervention strategies and it is this theory that is addressed in this report.

It is thought that the trend for tightly sealed, energy conscious homes, with fitted carpets and upholstered furniture creates traps for allergen that previously would have been removed by ventilation through ill-fitting doors and windows. This report assesses available research from around the world on indoor allergens and finds for the first time that fitted carpets are significant reservoirs of mite and pet allergens, whose importance has been underestimated in the past. These allergens play a major role, not just in triggering symptoms but in allergic sensitisation, especially during infancy - a sensitisation which is the very foundation of susceptibility to asthma and allergies in later life.

Prevalence of Allergic Diseases Across the World
Studies in different populations have shown that up to 85% of people with allergic asthma, but only 5-30% of the non-asthmatic population are allergy skin prick test positive to mites. Up to 100,000 mites may live in one square metre of carpet. People are allergic to enzymes found in mite faecal pellets.

Mites and their allergens are found in many countries around the world. The variation in their numbers depends mostly on humidity levels. For example, the level of mite allergens in very cold or dry climates is generally low, whereas higher levels are found in the coastal areas of Europe and the USA, where the climate is more suited to mite reproduction. The highest levels are found in regions where the climate is suited to mite growth throughout the year, such as the eastern coasts of Australia, Singapore and South America.

Distribution of mite allergens
Mite allergens are often ubiquitously distributed throughout houses and are found at many sites that are free of live mites, although sites that mites colonise (beds, carpets, and soft furnishings) generally have the higher allergen levels. Mite populations and their allergens are usually found at their highest level per unit weight of dust in beds, but carpets can contain the largest reservoir in total amount of mite allergens in the house.

The presence of carpets in a home can dramatically increase the total mite allergen load compared to having smooth floors. One study showed that the mite allergen concentration in dust from carpets could be 6-14 times higher than that from smooth floors and in some homes could be as high as that found in mattresses. The concentration of mite allergen increases with increasing age of the carpet and the presence of a dog is associated with higher mite allergen concentrations than found in petless households. Long pile carpets contain significantly more mites than short pile carpets.

Distribution of pet allergens
Pets are the second most important cause of domestic allergy and over 50% of asthmatic children are sensitised to allergens of cats and/or dogs. Despite this, these pets are very common in our society and one or other is found in over 50% of homes in many countries. It has been suggested that up to one third of cat sensitised individuals live in a home with a cat.

The presence of fitted carpets is particularly strongly associated with high pet allergen levels. Even when a pet is removed from a home the allergen levels can remain significantly higher than a home which has never housed a pet. Carpet levels become extremely important in this situation, as should a cat sensitive person move into a home that has previously contained a cat or dog, the allergens will remain in any carpets left in the house and may cause allergic reactions. Cat allergen is also easily spread from home to home on the clothes of cat owners, thus accumulating in the carpets of even non-cat-owners.

In one study, dust from schools with carpeted areas contained more cat allergen than the non-carpeted areas. This problem gives a great deal of support to the idea that carpets should not be present in schools as they will increase the chances that pet sensitive children will be exposed to allergen concentrations which can trigger their allergic reactions.

Risk Factors - Mite Allergens
There is no doubt that exposure to allergens can bring about a sensitisation which could lead to allergies in later life. Once sensitised to mites, for example, the likelihood of an individual developing asthma is greatly increased. After adjusting for sensitisation to other allergens, the risk of house dust mite sensitised children having asthma approximately doubles for every doubling of the level of exposure to mite allergens.

Sensitisation is more severe in people who live in regions with high exposure levels, and, in turn, asthma is more severe in people who have become sensitised and are subsequently exposed to high allergen levels.

It is more difficult to demonstrate a direct relationship between mite allergen exposure and prevalence of asthma symptoms. Many other factors can influence the symptoms of asthma such as, other sensitivities, cigarette smoke, pollution and infections. Other allergic diseases have also been strongly linked to mite allergens.

One study demonstrates a clear dose response relationship between exposure to house mites and risk of atopic dermatitis. Another shows that house dust mite allergen can aggravate the symptoms of seasonal conjunctivitis. Several more studies link perennial rhinitis with exposure to house dust mite allergens in mite sensitive patients.

Infant Vulnerability
It is widely accepted that infants are most at risk of becoming sensitised. Studies have shown a significant association between increasing degree of sensitisation and increasing exposure during infancy. Thus the most important time for allergen levels to be low is in infancy.

There are now studies which indicate that maternal allergen exposure during pregnancy can influence the development of fetal immune responses, and also new, sensitive techniques have been able to measure mite allergen in amniotic fluid, suggesting that maternal allergen exposure during pregnancy may play a role in primary sensitisation.

Reducing Allergen Exposure
In all, exposure to domestic allergens is strongly associated with increased risk of allergic disease, and in some cases increased symptoms. This must give strong support to the need to find effective methods of allergen reduction in homes, both for primary prevention of disease and alleviation of symptoms.

If we are to reduce the extremely high prevalence of allergic disease seen in many countries, and improve the quality of life of sufferers, we need to employ effective allergen reduction programmes.

Techniques to reduce allergen concentrations during infancy have the best chance of reducing the risk of asthma. Measures to reduce sensitisation can also be employed to manage established disease.

Epidemiological studies suggest that 2-fold reduction of allergen exposure at a community level would significantly reduce rates of sensitisation in early childhood, halve the risk of asthma development in sensitised children and similarly reduce asthma severity in clinical terms.

The best results for reducing exposure to house dust mite allergens have been achieved with a combination of encasing bedding and removing carpets and soft furnishings. Obviously allergen control measures need to be directed primarily towards sites in the home that contain most respirable allergen and where people spend most of their time. In most homes this means the living room and bedroom.

Control of Allergens in the Domestic Environment
This report reviews the effectiveness of a number of treatments for fitted carpets. These include acaricidal treatment, disinfectants and detergents such as benzyl benzoate, and tannic acid. The results were not dramatic and were not maintained for long periods of time. The overall conclusion was that if carpets cannot be removed alternative treatments to these will need to be found.

Steam cleaning was found to be very effective at reducing both mite numbers and allergen in the laboratory, but was less effective in real homes. Intensive vacuuming, shampooing and autoclaving of carpet pieces in the laboratory was also very effective in reducing mite allergen, but only autoclaving reduced live mites. Unfortunately, the most effective methods are not practical techniques for fitted carpets in the home, and the vacuuming and the shampooing were less effective and very intensive.

Large reductions in mite densities in beds and carpets were achieved in a controlled clinical trial with adult asthmatics using liquid nitrogen and vacuum cleaning. Unfortunately, the process can only be carried out by an operator who is fully trained in safety aspects of the use of liquid gases.

Overall, studies of mite allergen reduction in fitted carpets are very disappointing. The best results were obtained in the laboratory with little translation into effectiveness in the domestic environment. The most promising results are seen with intensive vacuum cleaning, but this is probably not practical outside a research setting, on fitted carpets in a real home. Several of the authors commented on these disappointing results in carpets.

The Importance of Carpet Removal It was notable that no study was able to reproduce the 10 fold difference between mite allergen concentrations seen between carpeted floors and uncarpeted floors reported from a study in Melbourne.

Surprisingly, very few studies have incorporated carpet removal into their interventions. The majority of successful clinical trials have either removed the carpets or treated them exhaustively with other cleaning methods. Of the 20 trials reported here, 7 showed significant clinical improvements (and two more showed a decrease in bronchial hyperreactivity. Of the 7 with notable improvements in symptom scores and medication usage, 4 removed the carpets, 1 treated them rigorously with liquid nitrogen , 1 with benzyl benzoate + encasing the mattress and the final one employed a punishing allergen avoidance regimen in the children's bedrooms. This study may also have removed carpets, but it is not made clear in the methods.

All the above studies concentrated on house dust mite allergen, but it cannot be ignored that cat allergen is the second most common trigger of asthma symptoms in the UK. A recent study showed that intensive cleaning with a high efficiency vacuum cleaner can significantly reduce cat allergen, which would still lead to an improvement in clinical symptoms even if sufferers are sensitive to both cat and mite allergen.

Carpet Usage
The UK has the highest consumption of carpets in Western Europe and North America, at 3.9 m2 per person, nearly twice as much as the next highest carpet consumers, The Netherlands and Germany, at 2.6 m2 per person. In contrast, Finland, Norway and Sweden consume only 0.4 m2 per person between them; in these countries the major trigger of asthma is cat and not mite allergen. It has also been reported that 98% of British homes have fitted carpets, compared with 16% in France and 2% in Italy.

Conclusion
This report has concentrated on the indoor environment and the allergens that accumulate in domestic situations. There is no doubt that there is a dose response relationship between the level of exposure to house dust mite allergens and the risk of becoming sensitised to mites, and that exposure of sensitised individuals is associated with a risk of developing asthma.

If we are to reduce the extremely high prevalence of allergic disease seen in many countries, and improve the quality of life of sufferers, we need to employ effective allergen reduction programmes. The best results for reducing exposure to house dust mite allergens have been achieved with a combination of encasing bedding and removing carpets and soft furnishings.

Fitted carpets, once in place, can be treated with rigorous allergen reduction measures, but these are much more difficult and time consuming than installing encasings for the bed. If people are prepared to follow daily cleaning regimens with effective products, then allergen reduction can be achieved, but such rigorous cleaning is unlikely to be practical for most people. Ultimately, the removal of fitted carpets, which are difficult to treat sources of allergen, is likely to be most practical and beneficial in the long term. Serious consideration now needs to be given to alternative furniture and flooring in order to persuade people to alter, what is, a deeply rooted, cultural practice.

Fitted Carpets and allergens

• Mite populations and their allergens are usually found at their highest level per unit weight of dust in beds, but carpets can contain the largest reservoir in total amount of mite allergens in the house.

• The presence of carpets in a home can dramatically increase the total mite allergen load compared to having smooth floors.

• Up to 100,000 mites may live in one square metre of carpet.

• One study showed that the mite allergen (Der p 1) concentration in dust from carpets could be 6-14 times higher than that from smooth floors and in some homes could be as high as that found in mattresses.

• The presence of fitted carpets is particularly strongly associated with high pet allergen levels.

• One study showed that dust from schools with carpeted areas contained more cat allergen (Fel d 1) than the non-carpeted areas. This problem gives a great deal of support to the idea that carpets should not be present in schools as they will increase the chances that pet sensitive children will be exposed to allergen concentrations which can trigger their allergic reactions.

• In studies where carpets were intensively treated to reduce mite allergen none of the methods used were able to reduce mite allergen concentrations by 90%, to match the low levels found in uncarpeted floors.

• It is striking that in all studies where there was significant benefit to allergy sufferers, carpets were either removed or were subjected to intensive treatment.

• The UK has the highest consumption of carpets in Western Europe and North America, at 3.9 m2 per person, nearly twice as much as the next highest carpet consumers, The Netherlands and Germany, at 2.6 m2 per person. In contrast, Finland, Norway and Sweden consume only 0.4 m2 per person between them; in these countries the major trigger of asthma is cat and not mite allergen.

• It has been reported that 98% of British homes have fitted carpets, compared with 16% in France and 2% in Italy.

• The UK has the highest prevalence of asthma symptoms in 13-14 year olds in the world, at 19.8%, the second highest prevalence of eczema and the twelfth highest for rhinoconjunctivitis.

See Statement to read the Healthy Flooring Network´s Statement of Concern,
and see the list of signatories.