Posted: December 2004
Thomas A E Platts-Mills
A primary objective for any physician treating patients with an allergic disease caused by or exacerbated by a specific allergen is to educate the patients about how to avoid the relevant allergens. The patient should understand the role that specific allergens play in causing symptoms and the measures that can be taken to reduce or avoid exposure. By doing so, they can gain control of their illness, reduce symptoms and in many cases they can reduce reliance on pharmaceutical products.
The evidence that avoidance of "indoor allergens" can help in the management of perennial rhinitis, asthma and atopic dermatitis is derived from two kinds of studies. First, where the patients are moved to a sanatorium or "allergen free unit" and second, where avoidance measures are taken in the patient's home (1, 2). Studies of the first type have been uniformly successful, whether they involved moving to an alpine village or a hospital room. By contrast, there has been a wide range of results with avoidance studies at home. Many such studies have not been successful; however, evaluation and analysis of those studies can help to identify the measures which should be recommended to patients who are allergic to specific allergens.
Allergen avoidance meta-analysis studies require careful evaluation of each study included. We believe that the published controlled trials of asthma that achieved a decrease in exposure to dust mites have been clinically beneficial (2). However, the primary outcome in many of the studies is to alter bronchial hyperreactivity (1, 2, 3). This parameter may not reflect the overall improvement that occurs with allergen prevention. Two studies in patients with allergic rhinitis and allergic asthma, which focused on mattress and pillow covers as a single measure to decrease mite exposure, reported negative results (New Eng J Med July 2003)(4,5). These results caused considerable confusion among doctors and patients, because they are well-controlled, large studies; because of their importance we will consider them further; however, both studies were seriously flawed (4, 5).
The primary reason why avoidance studies at home failed in earlier years is because the measures taken were inadequate. At least half of the studies published did not achieve a reduction in mite exposure. By contrast, when patients with asthma are admitted to an allergen-free environment, such as a hospital room, it is possible to reduce exposure by more than 95%, e.g., Der p 1, 13.4 μg/g, can be reduced to 0.3 μg/g. On the basis of avoidance studies performed in homes, the conclusion reached as early as the mid 1980s was that avoidance measures needed to be complete to achieve successful outcomes. For example, testing the effects of covers only, as reported in the recent study from the United Kingdom, is unlikely to succeed and indeed did not achieve significant decreases in mite allergens over one year (4).
Avoidance studies are plagued by behavioral effects induced by enrollment into the study (so called Hawthorne effects). These are different from placebo effects, because the family actually changes behavior because of enrollment so that real changes in allergen levels occur. Despite claims that the patients are enrolled into a "double blind controlled" trial, they always know that the study is about dust mites and dust mite control. Furthermore, they have heard a great deal about mites, and they can alter their behavior to try to "help" the study results or because they know they are being observed (6). In the recent trial from the Netherlands, in order to avoid this effect, all patients enrolled were instructed to wash bedding weekly in hot (60° C) water (5). However, this measure guarantees failure, as trying to test the effects of using covers when all the bedding is washed regularly is very unlikely to result in a successful outcome.
Since moving patients out of their homes into a "sterile" environment succeeds, it is simple to state that avoidance programs instituted in homes need to achieve similar results, i.e., a 95% decrease in exposure to the relevant allergen. However, this is not possible in the average home, and therefore, it is essential to focus on measures that are both possible and effective.
The first rule is that avoidance measures must be allergen specific. Even the most limited steps should only be recommended to subjects who have allergen-specific positive skin tests or positive assays for specific IgE antibodies. There is extensive anecdotal evidence about a large number of allergens, e.g., moths, crickets, molds, pets, rodents and others. However, the only scientific information available relates to dust mite, cat, and cockroach allergens. For each, allergen avoidance requires effort, and the measures recommended are different.
The quantity of dust mite allergen in a home is closely related to the growth of these microscopic Acarids. Their growth is critically dependent on humidity but also requires food (human skin scales) and sites for growth or nests (carpets, bedding, upholstered furniture and drapes). Mite allergen accumulation is in the form of fecal particles, and it is in this form that the allergens become airborne. In keeping with the size of these particles, mite allergens fall rapidly after disturbance, and for this reason, air filtration is ineffective in decreasing exposure to mite allergens.
To see video of the house dust mite, click here.
Controlling humidity: The strategies for controlling humidity depend entirely on the geographic location of the building or home. In areas with a dry climate, simply opening windows for one hour per day may be sufficient to keep the house dry. However, in warmer and humid locations, such as Florida or Georgia in the U.S.A., it is almost impossible to control humidity without central air conditioning. Even then, it is difficult to decrease the humidity sufficiently to adequately control dust mite growth. By contrast, in many areas of the USA that are less humid, basement dehumidifiers plus air conditioning can help to control mite growth.
Reducing "Nests": If humidity cannot be controlled, removing carpets, drapes, and upholstered furniture is an effective approach to control the production of mite allergens within a home. Although these measures are recommended, it is important to recognize the probable expense involved and to recommend them as medium or long term objectives.
Beds and bed covers: Controlling mite allergen accumulation in bedding can be achieved by regular washing alone or in combination with bed covers. Covering mattresses and pillows is an important method to prevent mites and allergens from contaminating the bedding but may also play an important role to prevent infestation. This became obvious from the unexpected finding that feather pillows contain less mites and mite allergens than synthetic pillows. Detailed investigation reveals that mites cannot penetrate through the tightly woven covers that are placed on feather pillows. In keeping with this observation, the finely woven covers which have pore size of approximately 6 μm are effective both at preventing colonization and allergen escape (8).
Washing: Regular washing is an effective method to control mite allergens. However, in a humid climate, mites will survive a cool wash and may flourish in blankets as well as drapes, knitted clothing or coats. Killing mites can be achieved by washing at high temperatures (i.e. 60° C = 140° F). However, this presents a problem where the temperature of the washing machines is determined by the temperature of hot water coming from the faucets. Furthermore, the American Academy of Pediatrics does not recommend water temperatures over 130° F because of the danger of causing burns in children. Therefore, the resulting temperature for washing is lower than that necessary to kill all of the mites. An alternative to hot water washing is to dry the clothing in a dryer at full temperature for 20 minutes or longer.
Removing Sundries: Apart from the obvious items in a bedroom, such as upholstered chairs, carpets and drapes, it is also wise to rid the room of soft toys and unnecessary clothing.
For patients who are both symptomatic and allergic by skin tests, the first priority is to encourage the family to find another home for the animals. Sometimes it is impossible to convince a patient or family to remove a pet. In that case, some of the recommendations listed below are helpful but much less effective than removing the animal(s) from the home.
The cat allergen, Fel d 1, is predominantly expressed in the cat's skin and is contained on skin flakes or "dander" of the cat. Fel d 1 has two properties that are highly relevant for avoidance: first, the particles are aerodynamically small enough to remain airborne for hours, and secondly, they are "sticky." The net result is that cat allergen is not only present in homes in which cats reside, but also present in schools and public buildings and even homes without cats. This raises the as yet unanswered question as to whether cat avoidance measures should be recommended for cat allergic patients who do not have a cat in their home.
With the cat in situ (9): The primary measure is to reduce reservoirs for cat allergens, such as carpets, sofas, drapes and blankets. Other measures will work only if these reservoirs are removed or extensively reduced.
Vacuum Cleaning: Regular vacuum cleaning is essential to prevent accumulation of allergens. However, it is important to have adequate filtration, including double thickness bags or HEPA filters on the cleaner outlet.
Washing the cat (or dog): Washing animals regularly removes large quantities of allergen, i.e., 2-3 mg of Fel d 1, but needs to be repeated regularly, perhaps as often as twice weekly. Washing is only possible with a few cats but is generally achievable with dogs.
Air filtration: The results using high efficiency particulate air filters illustrate the complexity of avoidance measures. If a high flow rate HEPA filter is placed on a carpet, which contains cat allergen, the likely result is an increase in airborne allergen because the airflow disturbs more allergen from the carpet than it removes from the air passing through it. The quantity of allergen airborne is measured in nanograms (i.e., 2-20 ng/m 3 ), while the quantity of cat allergen in the carpet or sofa maybe greater than 200 μg/g of dust, representing as much as 10 mg in a large carpet. Thus, although cat allergen, unlike mite allergen, remains airborne in an undisturbed home, the quantity airborne represents less that 0.01% of the allergen contained in the home.
Cockroaches are a pest in many homes and can reach extraordinary numbers. The primary determinants of cockroach growth are heat and the supply of food. In single-family homes, cockroaches are generally only a major problem in those areas where the outdoor temperature is sufficiently warm to allow these insects to live outside for several months of the year. By contrast, if buildings are heated year round, e.g., apartment blocks, hospitals or zoos, cockroaches can thrive in any geographic area.
Housekeeping practices influence cockroach infestation, since these insects are primarily attracted by human food and waste. They are less common in houses with a cat because the cats eat roaches. Whether mice or rats play a similar role is not clear. There are three elements to control cockroach infestation: insecticide baits, caulking to prevent access to an apartment, and control of food sources. The importance of an overall approach to avoidance is illustrated by the successful results of the recent controlled trial of avoidance among urban children with asthma (11).
Insecticides: There are a large number of insecticide sprays that can kill cockroaches and have been used in houses, but they are generally less effective and less acceptable than bait. Bait can be provided in traps where the insecticide is contained within a plastic protective casing. It is designed to be placed in the "normal" path for roach traffic. It is also available as a paste, which can be placed in small quantities in multiple sites where cockroaches live and reproduce. Several effective agents include boric acid and hydromethylnon. This chemical has been shown to significantly reduce cockroach infestation as a pest in the city of New York.
Preventing Access: Most families who live in large buildings consider or assume that it is impossible to prevent cockroach infestation. However, some eradication strategies include very aggressive caulking of the cracks or gaps around piping and other openings, particularly in apartment buildings or condominiums where cockroaches can move from one unit to another.
Encasing Food Supplies: Controlling access to food in the kitchen and throughout the rest of the home is a major aspect of cockroach control. Food should be fully enclosed or kept in a refrigerator. No waste should be kept in the home, and dishes or pans should not be left unwashed.
Cleaning: The brown stains from cockroach passage, saliva and feces in a home can be obvious. Less obvious is the large accumulation of cockroach allergens, sometimes present even without obvious signs of cockroach infestation. Aggressive "spring" cleaning may be necessary to reduce the cockroach allergen present in a home.
Avoidance of allergens remains a primary objective of allergy treatment. The measures recommended for each of the three major allergen sources discussed here are different. The evidence about avoidance applies only to patients who are allergic. Nonetheless, there are certain characteristics of a home that are helpful for controlling exposure to a range of allergens. These include minimizing allergen reservoirs such as carpets, sofas, and drapes that can become reservoirs for large quantities of allergen; keeping the home dry to prevent mold and bacterial growth as well as to control dust mites; and regular cleaning of surfaces so that there is less particulate matter to become airborne. Room air filters may be helpful but only if the reservoirs are appropriately controlled. Outdoor allergens, such as pollens and molds, can also be found indoors. A fan that blows outdoor air into the house can dramatically increase the quantity of outdoor allergens in a house.
Central to advice on allergen avoidance is the issue of how to convince patients to follow allergen avoidance measures. Home visitation is a very effective method to do so, not only because it is possible to provide practical advice, but also because it is the most effective method of persuading the patient about the need for change. Detailed advice with written instructions is essential. Visual aids are also useful. Allergen avoidance is the logical first step in managing allergic disease. Although it requires considerable time and effort, the benefits are often obvious and both the results and the education are appreciated by the patient.
(reproduced with permission from Karger: World Allergy Organization Guidelines for Prevention of Allergy and Allergic Asthma. Condensed Version. Johansson SGO, Haahtela T, et al. Int Arch Allergy Immunol 2004; 135:83-92) and Hogrefe and Huber: World Allergy Organization Guidelines for Prevention of Allergy and Allergic Asthma. Co Johansson SGO, Haahtela T, et al. Allergy Clin Immunol Int – J World Allergy Org 2004; 16:176-185)
House dust mite allergen reduction
Aims to reduce the amount of mite allergens in the home
Major strategies (WHO Strength of Recommendation A)
- Wash bedding regularly (every 1 – 2 weeks) at 55-60o C, if possible, to kill mites: (washing with cold water removes 90% of mite allergens; washing at 55-60o C kills mites)
- Wash pillows and duvets in hot water (55-60o C) and encase pillows and mattresses with protective coverings that have a pore size of 6 µm or less.
- Sufficient ventilation of dwellings to decrease humidity; aim to reduce indoor relative humidity to below 50% and avoid damp housing conditions
- Use a good quality vacuum cleaner (if possible, one fitted with HEPA filter)
- Use a damp duster when dusting and cleaning surfaces
- Replace wall to wall carpets with linoleum or wooden floors which can be wiped clean
- Remove/reduce curtains and soft furnishings in the bedroom
- Replace fabric-covered seating with leather or vinyl
- Remove soft toys from the bedroom; wash them at 55-60o C or freeze them (in a kitchen deep-freezer) to kill house dust mites
- Exposure of mattresses, rugs and carpets to direct strong sunlight (for more than 3 hours) kills mites and can be used in appropriate regions.
Provides mechanical barriers to pollen contact
- Keep windows closed at peak pollen times.
- Wear glasses or sunglasses to help prevent pollens entering the eyes
- Consider wearing a mask over nose and mouth to prevent inhalation of pollens at peak time
- Use air-conditioning where possible
- Install car pollen filters where possible
Pet allergen avoidance
Reduces the amount of pet allergen indoors
- If possible, find another home for the pet, and do not introduce new animals into the home. If the pet is not removed from the home, these measures may be helpful;
- Exclude pets from bedrooms and if possible keep pets outdoors
- Vacuum carpets, mattresses and upholstery regularly.
- Change clothes before going to school/work if you have had contact with any animal (for example, horse/cat/dog)
Cockroach allergen avoidance
Removes the cockroaches, eliminates the places and conditions in which they can live, and removes allergens
- Eradicate cockroaches with appropriate insecticide bait
- Seal cracks in floors and ceilings
- Enclose all food
- Do not store waste in the home
- Scrub floors with water and detergent to remove allergens
Mould allergen avoidance
Prevents mould from growin, and mould spores from becoming airborne during mould removal
- Use dehumidifiers in the home if relative humidity is constantly high (above 50%)
- Ensure heating, ventilation or air-conditioning systems are properly maintained
- Use 5% ammonia solution to remove mould from bathrooms and other contaminated surfaces
- Replace carpets with hard flooring; replace wallpaper with paint
- Repair indoor water damage immediately
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