Lesson 17, Volume 16—Indoor Allergen Control Measures: A Practical Summary

By Peter B. Boggs, MD

Objectives

1. Identify the most important indoor allergens affecting allergic asthma.
2. Understand and apply indoor allergen remediation measures in the care of allergic asthma.
3. Identify encasements shown to be effective barriers to house dust mite and pet allergens.
4. Identify laboratories that quantitate allergens in house dust samples.
5. Apply indoor allergen remediation check list to the care of patients with allergic asthma.

Key words

allergens; asthma; remediation measures

Abbreviations

CD = compact disc; HEPA = high-efficiency particulate air

The importance of reducing exposure to indoor allergens in the care of people with allergic asthma has been underscored in both the 1997 and 1999 National Asthma Education and Prevention Program guidelines^1,2 and in recent reviews.^3-5 Effective reduction measures should reduce the total quantity of allergen in the home, the allergen concentration in dust and other sources, and the exposure level of sensitive persons. Effective remediation should lead to reduced symptoms, diminished medication requirements, improved clinical well-being, and an enhanced quality of life.^3-5

The purpose of this article is to present a practical summary of indoor allergen remediation measures that can be effective in the care of people with allergic asthma. The role of indoor allergens as causal agents and triggers of asthma, and their remediation measures, have been extensively reviewed elsewhere^.4-10 Indoor allergen remediation measures summarized here include those for house dust mite, cat, dog, cockroach, and mold allergens.

Background

Avoidance of household allergens in the treatment of asthma was first recorded in the 16th century by Italian physician Gorolamo Cardano, who was called to Scotland by John Hamilton, Archbishop of St. Andrews, to advise on the treatment of the Archbishop's intractable asthma. Cardano, after reflection, recommended that the Archbishop remove his feather bedding. A "miraculous" remission followed.¹¹ Sir John Floyer observed in 1698 that asthma could be provoked by "…the sweeping of dust, especially in bedrooms."¹²

The first modern attempts to treat asthma by environmental intervention took place in the 1920s in the form of dust-free rooms, climate chambers, and cleaning measures designed to reduce dust in bedrooms.^13-15 The sentinel studies investigating the effect of environmental intervention on reducing allergen levels and improving asthma and allergy symptoms were done in alpine sanatoria in Switzerland and Italy.^16,17 Although burdened by the absence of controls, these investigators increased awareness of the importance of household agents as causes of asthma and allergy symptoms, and invited heightened attention to the most basic of treatments of allergic asthma: allergen avoidance.

Since that time, a series of immunologic, clinical, and epidemiologic studies have demonstrated a strong association between exposure and sensitization to indoor allergens and the development and persistence of chronic asthma in many areas of the world^.6-9,18

The relative importance of indoor allergens varies between and within cultures: cats and dogs are the dominant indoor allergens in Scandanavia and in desert regions of the United States; roaches in the inner city in the United States; and house dust mites in coastal, humid areas.³

Threshold levels (in micrograms of allergen per gram of settled dust) for sensitization and exacerbation of asthma for each of the common indoor allergens are incomplete. What is known regarding these levels will be cited in the discussion of each.

Past studies of the effectiveness of remediation measures in asthma suffer from being focused on single allergens, and hence are not representative of the more common clinical condition of multiple allergen sensitization.

Caveat

Indoor allergen avoidance programs for asthma care are only effective in the management of allergic asthma. The implementation of allergen avoidance measures in the management of nonallergic asthma is misguided and futile. Thus, a correct diagnosis of asthma and a proper assessment of airborne allergen sensitization are prerequisites to any remediation program.

The Five Common Indoor Allergens:
Effective Remediation Measures

Dust Mites

The house dust mite is the most important indoor allergen (Der p 1). It is ubiquitous in most humid areas. Although 13 species of house dust mite have been identified, only three are common in homes: Dermatophagoides farinae, Dermatophagoides pteronyssinus, and Euroglyphus maynei. Most mite infestations in the United States are caused by D farinae or D pteronyssinus; one species generally dominates in a home. Environmental control measures for house dust mites have been extensively reviewed^6,7 (see also "A Final Word" and American Academy of Allergy, Asthma, and Immunology handouts 1 and 2).

The phrase "snug as a bug in a rug" is a fitting description of the house dust mite's relationship to us and our living/working environments. Their basic needs—food, shelter, and a water supply—are easily met in the safety of our living spaces. Their main food sources are shed skin cells and the variety of organic debris commonly associated with house dust. They are sheltered by the nature of where they reside: deep in carpets, in beds, and in upholstered furniture. Mites exchange water, oxygen, and carbon dioxide through their general body surface, so water needs are met when the relative humidity is > 50%. The latter is easily accomplished in humid geographic regions and in homes with carpet and padding installed over a concrete foundation.

Remediation measures for house dust mite allergen (Der p 1) exposure can be divided into those that are highly effective (first-line or priority measures) and those that are only somewhat effective (second-line or alternative measures) (Table 1). The highly effective measures should be first priority in any remediation program and include encasements for pillows, mattresses, and box springs; hot (> 130°F) water washing of bedding once a week; removal of close contact reservoirs (stuffed toys); and avoidance of basements and other highly humid spaces as living areas.

Encasement of the pillows, mattresses, and box springs provides the simplest and most effective barrier to house dust mite exposure. Encasements shown to be effective barriers to mite allergen are readily available through mail-order houses (Table 2). Washing bedding once a week in hot water will both kill mites that have accumulated since the last washing and remove mite allergen. Caution is advised with such washing as water at this temperature is a scalding hazard. Adding detergents only slightly increases the efficiency of cleaning.19 Dry cleaning and tumble drying will both kill mites, but are less effective in the removal of mite allergen than wet cleaning.^20,21

Vacuuming removes bulk dust from the carpet, bed, and upholstered furniture, but does not kill mites and does not change the concentration of mite allergen per gram of settled dust.²² On the other hand, steam cleaning of the carpet and bed has been shown to be effective in both killing mites and reducing mite allergen.²³

Because the house dust mite allergen (Der p 1) particles become airborne only with significant disturbance and are carried on relatively large particles (10 to 20 mm), they are able to remain in the air for only a relatively short period of time (hang-time is < 30 min). Hence, most dust mite allergen exposure is the result of close contact (beds, stuffed toys). The second major exposure to dust mite allergen comes on vigorous disturbance of their habitat such as during vacuuming and cleaning.

Measures that have shown some effectiveness but are currently felt to be less effective than essential measures include controlling the humidity in the home (40 to 50% relative humidity); removing carpet from primary living areas and replacing it with polished surfaces; replacing draperies with easily cleanable surfaces; and replacing fabric furniture with vinyl or leather.^3,5,7 A variety of chemical agents (acaricides and denaturants) are available, but have not been shown to be particularly effective in reducing mite allergen.²⁴ Apparently an active compound in the laboratory does not equate with good results in the home.

The threshold levels for sensitization and exacerbation of asthma are 2 mg/g and 10 mg/g, respectively.²⁵

Caveats. House dust mites are microscopic and hence do not provide the visual clues important in gaining commitment to remediation programs. Additionally, mite-allergic people generally do not experience exacerbations during short visits (a few hours) in homes heavily infested with mites, in contrast to the cat-allergic person who visits a home with an indoor cat. These observations reflect the importance of skin testing to confirm IgE sensitization and the identification of allergen(s) present in the patient's house dust.

Cat and Dog Allergen

Cats and dogs are our most common animal cohabitants, present in more than one third of US homes. The cat currently enjoys the status of the most popular pet.

Cat and dog allergens are potent sensitizers. The major cat allergen is Fel d 1, which elicits IgE responses in > 90% of people with cat allergy. Cat albumin is also problematic, accounting for 20% of IgE responses in people with cat allergy. The major dog allergens are Can f 1 and Can f 2, accounting for 75 and 72.5%, respectively, of IgE responses in patients with dog allergy. About 25% of patients also have IgE responses to dog albumin. Fel d 1 and Can f 1 are small-molecular-weight proteins found primarily in animal secretions from sebaceous glands, sublingual salivary glands, perianal glands, and epithelial cells. Structurally, they belong to a family called lipocalins whose purpose is to sense and transport pheromones.²⁶

Aerodynamically, they are carried on particles ranging from 1 to 20 µm in diameter (15% are carried on particles < 5 mm) and can remain airborne for hours to days. This is in marked contrast to the house dust mite, cockroach, and mold allergens, which are carried on large, relatively heavy particles and thus are aerodynamically disadvantaged. The small, light cat and dog allergens are able to circulate on the air currents throughout homes, making it virtually impossible for any room to be "safe."^27,28

Cat allergen particles are also sticky, which leads to widespread distribution in the environment—walls, other surfaces, clothing—and in other places such as homes, workplaces, and schools in which pets have never lived.²⁹

The highly potent nature of pet allergens and their aerodynamic characteristics make remediation options short of total removal of the pet ineffective. Less aggressive measures have not been shown to significantly reduce allergen in settled dust or in the air. Simply said, no other clinical advice is appropriate.

Pet removal should be followed by repeated and extensive cleaning efforts to remove allergen that has fixed to surfaces. Encasement of pillows, mattresses, and springs with materials known to be impermeable to cat allergen is recommended (Table 3). High-efficiency particulate air (HEPA) room filters may also be helpful in removing airborne circulating pet allergen, but their impact on symptoms remains to be established.^30,31

So what does one offer the many pet lovers who are not willing to give up their pets? Compromise measures can be suggested, but should be placed in proper clinical context. Those likely to be somewhat helpful include use of room HEPA filters; isolation of pet to one to two rooms (not a bedroom); frequent (more than once/wk) washing of pet; washing clothing after it has come in contact with the pet; and never allowing a pet in the bedroom. Castration reduces Fel d 1 production but its effect on reducing symptoms is unclear.²⁶ Clinically, pet owners who do not remove pets from the home should have more persistent and severe symptoms with continuous exposure.

The threshold levels for cat (Fel d 1) allergen associated with a maximal risk of sensitization is between 1.7 and 23 mg/g of settled dust. The threshold level to trigger an exacerbation of asthma is unclear. Neither level has been defined for dog allergen.²⁵

Caveats. Even with repeated and extensive cleaning and remediation efforts, it can take up to 6 months after a pet has been removed to begin to see the impact of allergen reduction. Sadly, at this time, there is simply no way to rid an environment of cat or dog allergen short of removal of the pet followed by extensive and repeated cleaning efforts.

Cockroach

Although there are some 3,500 identifiable species of cockroach, four commonly infest our homes: German, American, Oriental, and brown-banded.³²

Cockroaches prefer dark, snug places close to water and food, and they venture forth to scavenge at night. It is because of the latter that many people do not realize their homes are infested. A daytime sighting is unusual and reflects significant overcrowding of the reservoir with inadequate food and water supplies.

Multiple allergens have been identified as sensitizers for humans (Bla g 1, etc.). Allergen sources include cast skins, dead bodies, fecal material, saliva, and secretions. Cockroach feces and saliva are common calling cards. Although cockroach allergen is highest in kitchens, it is also found in beds, bedding, and sofas. Work and school environments are not immune to cockroach infestation.³²

Cockroach allergen requires a significant physical disturbance to become airborne. Like house dust mite and mold allergens, cockroach allergens are carried into the air primarily on large (> 10 mm) particles, most of which settle rapidly. However, recent studies have shown that some allergen is dispersed on smaller particles and can remain in the air for longer periods.²⁵ Additional studies are required to define the aerodynamics of cockroach allergen particles.

Effective remediation of cockroach allergens include professional extermination (initial and at least one follow-up in about 2 weeks) and aggressive cleaning before and after extermination to reduce allergen and food sources, including thorough vacuuming (Table 4).32 Encasements impermeable to house dust mite and cat allergen are impermeable to cockroach allergen as well. Secondary measures are common sense and include the daily washing of dishes and removal of garbage; storing food in sealed containers (plastic or glass); sealing plumbing openings, cracks, and crevices; and the placement of bait traps. HEPA filters may help with elimination of the smaller airborne allergens.

Threshold cockroach allergen studies suggest that levels > 2 mg/g of dust are sufficient for sensitization in a genetically susceptible person and levels > 8 mg/g of dust can trigger asthma symptoms.²⁵

Caveats. Cockroach allergens may remain in settled dust for many months after successful extermination and will require repeated cleaning for removal.32,33 Successful extermination and allergen elimination are not the same thing: allergens can persist indoors for months after successful extermination. The best one can hope for is a 95% reduction in cockroach allergens. Hence, it is more difficult to achieve clinical control of cockroach allergy with heavy infestations. Successful cockroach extermination generally requires the participation of professional exterminators.

Mold

Although there are more than 200 species of known fungi, relatively few play any role in causing or triggering asthma. Several species predominate in homes: Alternaria, Cladosporium, Epicoccum, Fusarium, Penicillium, and Aspergillus. During the cold months, Aspergillus and Penicillium predominate.³⁴

Household molds flourish by finding sufficient water and food in common indoor materials: furniture, carpet, paneling, clothing, house dust, cellulose in paper goods, glues, wood, insulation materials, heating and air conditioning systems, etc. Environments in homes that commonly invite mold growth include bathrooms, basements, food and supply storage rooms, and attics.²⁵

Water and humidity are the keys to both mold survival and the success of mold allergen control (Table 5). Essential remediation measures include the repair of water leaks and leak-damaged areas; limiting the relative humidity to 50% via use of air conditioning and installation of dehumidifiers; provision of adequate ventilation of high-humidity living spaces; increasing available natural light; and cleaning surfaces on which visible mold is accumulating. Secondary remediation measures include discarding moldy items; maintenance of heating, ventilation, and air conditioning systems; room air filtration; and good ventilation of areas of high humidity (bathroom and kitchen).²⁵

Mold exposure in homes occurs through airborne spores and hyphal fragments. Release is generally dependent on direct mechanical disturbance. The particle sizes of airborne spores and hyphal fragments range from 2 to > 50 mm; thus, although most are believed to settle as rapidly as house dust mite and roach particles, some do not.²⁵

Caveats. Water and humidity control, adequate ventilation of living spaces, and the provision of adequate lighting are the keys to effective remediation. Together, they can be remembered as the 3 D's of mold control: dampness, drafts, and darkness.

Commitment to Environmental Allergen
Avoidance Measures

Anyone engaged in the long-term care of patients with allergic asthma is aware that adult patients and parents of children with asthma generally are less committed to remediation efforts than is required for optimal impact. Studies have confirmed this low level of commitment.^35,36 The ingredients needed to invite high levels of commitment are not clear. Helpful to the achievement of commitment are simple, clearly explained suggestions; a good relationship between physician and patient; emphasis on essential measures rather than secondary measures; follow-up visits with progress reports and positive reinforcement; and the quantitation of baseline and follow-up allergen levels in settled dust with feedback to the patient. Both patient and physician should be familiar with the pitfalls that accompany indoor allergen control (Table 6).

What's Coming?

At the present time, we are able to measure the relevant allergens present in settled dust of homes, schools, workplaces, etc (Table 7). Investigators are working on personal monitors that will better define to which indoor allergens we are most exposed.³⁷ Integrating this new knowledge with what is already known of the effectiveness of environmental controls should be most helpful in the long-term management of allergic asthma.

A Final Word

At the last meeting of the American Academy of Allergy, Asthma, and Immunology, a compact disc (CD) was made available that contained the handouts from each session of the meeting. This CD contains a number of very thorough outlines/reviews of environmental allergens and their remediation measures by investigators active in this field. These materials were used liberally in the preparation of this summary. An indoor allergen remediation measure check list based on the reviews in this CD is provided in Table 8. This CD is highly recommended and may be obtained at no cost through the American Academy of Allergy, Asthma, and Immunology (611 East Wells St, Milwaukee, WI 53202-3889; telephone: 414-272-6071; e-mail: info@aaaai.org).

Particularly helpful are the following handouts:

1. Bush RK. Allergens in indoor environments: iIdentification and removal.
2. Bush RK. Allergen abatement: what really works? Control of fungi.
3. Custovic A. Prospective controlled trials of allergen avoidance.
4. Custovic A. Control of animal allergens.
5. Eggleston PA. Control of environmental allergens as a therapeutic approach.
6. Eggleston PA. Methods and effectiveness of indoor environmental controls.
7. Platts-Mills TAE. Lifestyle factors affecting asthma around the world.
8. Platts-Mills TAE. Inhaled allergen exposure and asthma.
9. Tovey E. Control of dust mite allergens.

Table 8 is a check list of indoor allergen remediation measures based on these reviews.

References

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