Environmental control and the management of allergic diseases

As many as 50 million Americans suffer from an allergic disease. Although sensitization and symptom development are multifactorial, exposure to aeroallergens is a significant contributor to allergic rhinitis (AR), asthma, atopic dermatitis, and other allergic diseases. Recent technological developments such as monoclonal antibody-based assays permit the determination of an individual's sensitization to specific allergens, measurement of the level of allergens in dust and air samples, and evaluation of the effectiveness of measures to reduce allergen exposure. This article addresses the current understanding of the prevalence of aeroallergens; the association between exposure, sensitization, and disease; important allergens and irritants in our environment; and environmental control methods. The role of house dust in allergic reactions is not new. Kern 23 reported an association between dust exposure and asthma in 1921. At the present time, it is estimated that 20% of the population has immediate hypersensitivity to at least one aeroallergen. A recent study followed children from birth to the age of 3 years, evaluated total serum IgE and sensitivity to dust mite and cat allergens, and measured allergen levels in house dust. The authors reported that early development of allergen sensitization was related to elevated levels of these allergens in the home. Wahn et al 57 also suggested that children with an allergic immediate family member are at risk for sensitization from exposure to even low allergen levels. AR effects 10% to 20% of the population, with peak onset in childhood and adolesence. This disease has significant direct and indirect costs. Although the direct cost of care for AR is estimated at $6 billion per year, Ross 48 estimates the loss of work productivity at an additional $4 billion per year. AR is also a contributing factor in sinusitis, otitis media, and nasal polyps. McMenamin 30 estimates the cost of these complications of AR at $10 billion per year. The adverse effect of AR on quality of life and learning in children is also significant. Patients with AR report sleep loss, decreased concentration, and decreased social interaction. Children with AR experience learning impairment because they are absent from school or fatigued, irritable, or distracted by their symptoms or medications. 50 Allergy has been causally related to asthma as well. As many as 85% of children with asthma and half of adults with asthma have sensitivity to at least one inhaled allergen as determined by skin testing. Further, the incidence of asthma has risen dramatically in the past two decades, and increased time indoors and exposure to allergens are thought to be contributing factors. Patients admitted to the emergency department with acute asthma have been shown to be both sensitized and exposed to allergens in their homes. 3,16,45 A prospective study of children from birth to the age of 11 years who had at least one allergic parent found that children with high dust mite allergen levels in the home started wheezing at a younger age than children with a similar background whose allergen levels at home were low. Further, the children in the high allergen homes were significantly more likely to be wheezing at age 11 than their cohorts in low allergen environments. 51 Cloosterman et al 6 suggest that the development of symptomatic asthma from subclinical asthma may be attenuated by house dust mite avoidance in dust mite-sensitive patients. In response to these and other epidemiological studies, the National Institutes of Health Heart, Lung, and Blood Institute Expert Panel Report 2 recommends testing for perennial allergen sensitivity by skin testing or in vitro testing in persons with persistent asthma. 17 The allergens associated with allergic diseases vary from location to location. Dust mites have been studied the most extensively; however, recent studies have reported the role of other indoor allergens in asthma. For example, cockroach allergen levels exceed dust mite allergen levels, and exposure to cockroaches is an important risk factor for acute exacerbation of asthma for persons living in low-socioeconomic, urban, multifamily dwellings. 47 Exposure to household pets such as cats and dogs is associated with asthma in homes at high altitudes 22 and in extremely cold climates. 61 Changes in home construction and furnishings and an increase in time spent indoors (as much as 23 h/d) are thought to contribute to the increase in asthma morbidity. In response to the energy crisis of the 1970s, homes are now built to be more efficient, with tighter construction, fewer air exchanges, central heat, warmer temperature, and higher relative humidity, as well as more carpeting and upholstered furniture. These changes provide breeding environments and reservoirs for indoor allergens and increased levels of irritants such as gases, particulates from wood stoves, and volatile organic compounds (VOCs). 41,44 Reduction of allergen exposure is associated with a decrease in symptoms and delayed onset of sensitization and disease. When dust mite allergic asthmatics are moved from homes with high allergen levels to an environment where house dust mite avoidance modifications are in place and allergen levels are low, their asthma symptoms, measures of bronchial hyperreactivity and lung function, and medication usage improve. 5,15,34,43,58 Thus, an important component of the management of allergic disease is reduction or elimination of allergen exposure, one major factor in chronic inflammation of the airway.