Effect of mattress and pillow encasings on children with asthma and house dust mite allergy

Progress in the management of childhood asthma

Asthma has become the most common chronic disease in childhood. Significant advances in epidemiological research as well as in therapy of pediatric asthma have been made over the past 2 decades. In this review, we look at certain aspects therapy of childhood asthma, both in the past and present. Literature review on allergen avoidance (including mites, cockroach and cat), intensive therapy with β(2)-agonists in acute asthma (administering via continuous nebulization and intravenous routes), a revisit of theophylline use and its action, the use of inhaled corticosteroids in various phases of childhood asthma and sublingual immunotherapy in asthma are examined. Recent facts and dilemmas of these treatments are identified along with expression of our opinions, particularly on points of childhood asthma in the Asia-Pacific, are made in this review.

Impact of environmental controls on childhood asthma

Exposure to allergens early in life can lead to sensitization and the development of childhood asthma. It is thought that increased exposure with the advent of modern housing is likely contributing to the rise in prevalence of childhood asthma during the past few decades. The progression from allergen exposure to sensitization and asthma development has been noted with respect to dust mites, pets, cockroach, mouse, mold, tobacco smoke, endotoxin, and air pollution, although some have found a protective effect with pet and endotoxin exposure. Recent studies have shown that allergen remediation may be beneficial in reducing asthma morbidity and development, although there is also some evidence to the contrary. Examples of allergen remediation that have been studied include the use of dust mite-impermeable covers, high-efficiency particulate air filtration, integrated pest management, home repairs, ventilation improvement, and pet removal. Several multifaceted, randomized controlled trials have shown that reducing multiple early allergen exposures with environmental controls is associated with a decreased risk of asthma.

What Is the Evidence That Environmental Remediation Programs Are Effective in Urban Children With Allergic Asthma? An Integrated Review

Children with allergic asthma living in urban areas are exposed to heavy loads of allergens that adversely affect their health. The purpose of this inquiry was to determine if environmental remediation programs for urban exposures are effective. Research articles relevant to this topic were obtained by conducting a literature search of the Cumulative Index of Nursing and Allied Health Literature, PubMed Plus, and Google Scholar databases. Search terms included combinations of asthma, environmental remediation, environmental triggers, environmental interventions, urban, and allergies. Out of 27 articles retrieved, 14 meeting inclusion and exclusion criteria were retained. When considered together, it appears that multiple-trigger environmental remediation programs are more effective than single- trigger programs in reducing asthma morbidity. To produce the best outcome, these programs should be tailored to a child’s specific sensitization and exposure. Asthma educators play a role in allergen remediation programs, beginning with educating their patients about environmental triggers and referring them, as needed, to more intensive remediation programs and resources.

The indoor environment and its effects on childhood asthma

PURPOSE OF REVIEW

Indoor pollutants and allergens cause asthma symptoms and exacerbations and influence the risk of developing asthma. We review recent studies regarding the effects of the indoor environment on childhood asthma.

RECENT FINDINGS

Exposure to some indoor allergens and second hand smoke are causally related to the development of asthma in children. Many recent studies have demonstrated an association between exposure to indoor pollutants and allergens and airways inflammation, asthma symptoms, and increased healthcare utilization among individuals with established asthma. Genetic polymorphisms conferring susceptibility to some indoor exposures have also been identified, and recent findings support the notion that environmental exposures may influence gene expression through epigenetic modification. Recent studies also support the efficacy of multifaceted environmental interventions in childhood asthma.

SUMMARY

Studies have provided significant evidence of the association between many indoor pollutants and allergens and asthma morbidity, and have also demonstrated the efficacy of multifaceted indoor environmental interventions in childhood asthma. There is also a growing body of evidence suggesting that some indoor pollutants and allergens may increase the risk of developing asthma. Future studies should examine mechanisms whereby environmental exposures may influence asthma pathogenesis and expand the current knowledge of susceptibility factors for indoor exposures.

Indoor allergen levels in Guangzhou city, southern China

BACKGROUND

  High levels of sensitization to house dust mites have been observed in Chinese allergic patients. This study has measured levels and distributions of mite and cockroach allergens in household dust in Guangzhou. Influences of home characteristics and seasonal changes on allergen levels were also investigated.

METHODS

  Dust samples were collected from bedding and living room from households in Guangzhou. Major allergens from Dermatophagoides pteronyssinus, D. farinae, D. microceras, Blomia tropicalis and cockroach allergens were measured by ELISA. Home characteristics were obtained from a questionnaire.

RESULTS

  Four hundred and four dust samples were collected from 107 homes during October 2006 to November 2007. House dust mite allergen levels were detectable in 99% of the bedding samples. Der f 1 levels were significantly higher than Der p 1 levels. High levels of mite allergens (>10 μg/g) were observed in 88% of all the bedding samples. Cockroach allergens were detected in 93% of households and were higher in living room samples than in bedding samples. Blo t 5 and Der m 1 could not be detected in the dust samples. Having fabric furniture was a predictor of high allergen levels. Der f 1 levels were higher in summer time than in winter time. Cockroach allergens were higher in winter time than in summer time.

CONCLUSION

  In Guangzhou, Der f 1 is the predominant mite allergen in dust with very high levels in bedding. Cockroach allergens are also common.

[Secondary and tertiary prevention of allergic asthma in children]

Asthma is a disease of the lung epithelial barrier, most often associated with allergy in children. Asthma and allergy are two distinct diseases, but the phenotypic expression of asthma depends on atopic status. A better definition of phenotypes of asthma would result in better targeting of prevention and treatment modalities. Secondary prevention aims to prevent the onset of asthma and the acquisition of new sensitizations in sensitized children. Studies concerning allergen avoidance are insufficient to reach a definitive conclusion and antihistamines have not been shown to be effective. The results for specific immunotherapy suggest a benefit to prevent transition from allergic rhinitis to asthma and the onset of new sensitizations. Tertiary prevention aims to reduce symptoms in children with an existing allergic asthma diagnosis. The avoidance of known respiratory allergens will only be effective in combination with management of the whole environment. Specific immunotherapy has a real place, in combination with background therapy. It should be used according to guidelines in appropriately treated patients.

Outpatient management of asthma in children age 5-11 years: guidelines for practice

PURPOSE

To increase awareness among nurse practitioners (NPs) regarding diagnostic and treatment guidelines for asthma for the 5-11 year age group recently updated by the National Asthma Education Prevention Program-Expert Panel 3 (NAEPP-EPR3).

DATA SOURCES

NAEPP-EPR3 guidelines for the diagnosis and management of asthma released from the National Heart, Lung, and Blood Institute in August 2007, selected clinical trials, meta-analyses, and clinical reviews.

CONCLUSIONS

Recent research has revealed that children suffering from asthma in the United States are underdiagnosed and their asthma is poorly controlled. Compelling evidence supports that children classified as having persistent asthma following NAEPP-EPR3 guidelines benefit from daily inhaled corticosteroid therapy, yet many are misclassified and undertreated.

IMPLICATIONS FOR PRACTICE

With application of current guidelines from NAEPP-EPR3, NPs can more effectively assess, diagnose, treat, and foster a collaborative self-management plan for children age 5-11 years. These interventions will result in an improved quality of life and decreased health risks for this young population.

House dust mite control measures for asthma: systematic review

The major allergen in house dust comes from mites. We performed a systematic review of the randomized trials that had assessed the effects of reducing exposure to house dust mite antigens in the homes of people with mite-sensitive asthma, and had compared active interventions with placebo or no treatment. Fifty-four trials (3002 patients) were included. Thirty-six trials assessed physical methods (26 mattress covers), 10 chemical methods and eight a combination of chemical and physical methods. Despite the fact that many trials were of poor quality and would be expected to exaggerate the reported effect, we did not find an effect of the interventions. For the most frequently reported outcome, peak flow in the morning (1565 patients), the standardized mean difference was 0.00 (95% confidence interval (CI) -0.10 to 0.10). There were no statistically significant differences in number of patients improved (relative risk 1.01, 95% CI 0.80-1.27), asthma symptom scores (standardized mean difference -0.04, 95% CI -0.15 to 0.07) or in medication usage (standardized mean difference -0.06, 95% CI -0.18 to 0.07). Chemical and physical methods aimed at reducing exposure to house dust mite allergens cannot be recommended.

House dust mite control measures for asthma

Editorial note

This 2011 review predates current reporting standards and methodological expectations for Cochrane Reviews. It should not be used for clinical decision‐making.

BACKGROUND

The major allergen in house dust comes from mites. Chemical, physical and combined methods of reducing mite allergen levels are intended to reduce asthma symptoms in people who are sensitive to house dust mites.

OBJECTIVES

To assess the effects of reducing exposure to house dust mite antigens in the homes of people with mite-sensitive asthma.

SEARCH STRATEGY

PubMed and The Cochrane Library (last searches Nov 2007), reference lists.

SELECTION CRITERIA

Randomised trials of mite control measures vs placebo or no treatment in people with asthma known to be sensitive to house dust mites.

DATA COLLECTION AND ANALYSIS

Two authors applied the trial inclusion criteria and evaluated the data. Trial authors were contacted to clarify information.

MAIN RESULTS

Fifty-four trials (3002 patients) were included. Thirty-six trials assessed physical methods (26 mattress encasings), 10 chemical methods, and 8 a combination of chemical and physical methods. Despite the fact that many trials were of poor quality and would be expected to exaggerate the reported effect, we did not find an effect of the interventions. For the most frequently reported outcome, peak flow in the morning (1565 patients), the standardised mean difference was 0.00 (95% confidence interval (CI) -0.10 to 0.10). There were no statistically significant differences either in number of patients improved (relative risk 1.01, 95% CI 0.80 to 1.27), asthma symptom scores (standardised mean difference -0.04, 95% CI -0.15 to 0.07), or in medication usage (standardised mean difference -0.06, 95% CI -0.18 to 0.07).

AUTHORS' CONCLUSIONS

Chemical and physical methods aimed at reducing exposure to house dust mite allergens cannot be recommended. It is doubtful whether further studies, similar to the ones in our review, are worthwhile. If other types of studies are considered, they should be methodologically rigorous and use other methods than those used so far, with careful monitoring of mite exposure and relevant clinical outcomes.

Inner-city asthma: the role of the community

Asthma morbidity and mortality are disproportionately high in low-income minority populations. Variations in environmental exposures, stress, and access to appropriate health care all contribute to these disparities. The complex nature of asthma with strong contributions from environmental, psychosocial, and biological factors suggest that community-based approaches focused on the unique needs of high-risk populations may be effective. The few previous randomized trials suggest that case management with professionals and/or community health educators may reduce asthma morbidity. Health-educator programs should be lodged in stable infrastructures with training and funding for community health workers to obtain long-term sustainability. Factors not amenable to individual intervention, however, such as poor condition of homes, outdoor pollution, and lack of access to appropriate care, will require collaborative efforts of community groups, academic professionals, public agencies, and health-care providers.

Sensitisation to aeroallergens in Brazilian adolescents living at the periphery of large subtropical urban centres

OBJECTIVES

To evaluate the sensitization to aeroallergens determined by skin prick test (SPT) in Brazilian adolescents, and to correlate its positivity with the diagnosis of asthma and/or rhinitis based on the written questionnaire (WQ) of ISAAC phase III study.

PATIENTS AND METHODS

A total of 996 adolescents (387 boys) were selected by systematic samples. A standard allergen extracts panel (positive/negative control, D pteronyssinus [Dpt], P americana [Pa], B germanica [Bg], dog, cat, fungal and grass mix) was used and its positivity compared with positive responses to asthma, rhinitis or both.

RESULTS

Positive SPT to at least one allergen was observed in 466 adolescents (46.8 %), with sensitisation to Dpt in 79.1 %. Positivity to more than one allergen occurred in 232 students (49.8 %). The frequency of positive SPTs was significantly higher among adolescents with asthma (OR = 2.16), rhinitis (OR = 1.69), and asthma and rhinitis (OR = 2.03). Positive SPT to four or more allergens were higher among asthmatics (OR = 2.6) and among adolescents with asthma and rhinitis (OR = 3).

CONCLUSIONS

A high sensitisation rate to aeroallergens was observed, significantly higher among those with asthma, rhinitis or a combination of both, especially in multiple sensitisations.

Impact of home environment characteristics on asthma quality of life and symptom scores

We explore the relationship between home-based triggers, asthma symptoms, and quality of life (QOL) with data from 177 adult and pediatric participants who received a home environmental assessment. Outcomes included the Asthma Quality of life Questionnaire, the Prediatric Asthma Quality of Life Questionnaire, the Paediatric Asthma Caregiver's Quality of Questionnaires and the Lara Asthma Symptom Scale. The absence of roaches and the use of dust mite covers were positively associated with QOL in pediatric and adult participants. Frequent bed sheet washing was associated with increased symptoms and decreased quality of life in adults and caregivers of pediatric participants. These findings confirm existing wisdom on roaches and dust mite covers and raise important questions about bed sheet washing recommendations.

Room-specific characteristics of suburban homes as predictors of indoor allergen concentrations

BACKGROUND

Room characteristics predicting indoor allergen exposure in suburban homes have not been clearly identified.

OBJECTIVE

To examine relationships between room characteristics and concentrations of indoor allergens in homes of suburban asthmatic patients.

METHODS

The homes of 339 asthmatic children ages 6 to 17 years were studied. Home inspections were conducted by a trained technician, and dust samples were analyzed for indoor allergen content. A high allergen concentration was defined as 8 microg (U)/g or more of fine dust.

RESULTS

Infrequent sheet washing and wall-to-wall carpet were risk factors for high bedroom dust mite concentrations. Infrequent sheet washing was also a risk factor for high Fel d 1 concentrations. Food remains in the bedroom was a risk factor for high bedroom Bla g 1 levels, and exposed food, leaks, and dirty pots were all risk factors for high kitchen Bla g 1 levels. The combination of lack of mattress or pillow encasements, infrequent sheet washing, and carpeting was associated with a 24-fold increase in odds of a high dust mite concentration (odds ratio [OR], 24.1; 95% confidence interval [CI], 3.2-181.4). Among non-cat owners, the combination of stuffed toys on the bed, lack of mattress or pillow encasements, and infrequent sheet washing was associated with a 49-fold increase in odds of a high Fel d 1 level (OR, 49.4; 95% CI, 2.8-887.3). The combination of leaks, exposed food, and dirty pots was associated with a high kitchen Bla g 1 concentration (OR, 10.6; 95% CI, 2.8-40.5).

CONCLUSIONS

Specific room characteristics predict high indoor allergen exposure among children with asthma, and a combination of these characteristics may further increase the risk of high allergen exposure.

Dust mite allergen avoidance as a preventive and therapeutic strategy

Asthma is a global health problem with genetic and environmental components. Indoor allergens have a major impact on asthma, and exposure in sensitized subjects can compromise lung function. A reduction in allergen exposure would seem a logical facet to treatment. Methods for reducing mite allergen levels that are effective in the laboratory may not work in the home and may not result in a clinical benefit. Six ongoing studies are investigating the effects of environmental control on the primary prevention of asthma and allergies. Although the Isle of Wight and Canadian studies provide encouraging results at age 8 and 7 years, respectively, it will be some time before a definitive public health message emerges. For secondary prevention, there is little evidence to support the use of mite-proof encasings as a single intervention in adults. In children, however, single or multifaceted interventions appear to be of some benefit.

Effect of home environment control on children with atopic or non-atopic asthma

BACKGROUND

Although allergen avoidance is known to be important for treating atopic diseases, there is a very limited amount of time for clinical education of patients on this topic.

METHODS

We compared the effect of the thorough home visit counseling (>60 minutes per visit) for avoiding house dust mites (HDMs) with that of regular guidance in our clinics (10 minutes per patient). We enrolled 36 children with asthma (7 years of age or younger; mean, 3.8) in this study under an informed consent. After enrolling the 24 patients for the home visit, 12 families were enrolled as controls for the regular clinical guidance. Between June 1995 and June 1996, we visited the homes of 24 children with asthma enrolled in this study every month and performed a thorough HDM-avoidance counseling of more than 60 minutes (home visit counsel) at each visit. We compared the effects of this counseling with those of the regular clinical guidance given (10 minutes per patient) to the remaining 12 children with asthma. We also evaluated the effect of home visit counseling on children of two subgroups, i.e., an atopic (with positive IgE antibody against HDM) and a non-atopic (without detectable IgE antibodies against 8 common allergens) subgroup.

RESULTS

Home visit counseling markedly reduced the frequencies of asthma attacks (p < 0.000001), the required theophylline dosages (p < 0.0005), and the levels of HDM allergens (p < 0.0005) in the atopic subgroups, whereas the effect of regular counseling on these 3 items was relatively less (p < 0.05 or not significant). Surprisingly, home visit counseling also markedly reduced the asthma attacks (p < 0.00001) and theophylline dosages (p < 0.00001) of children with non-atopic asthma.

CONCLUSIONS

These results suggest that thorough allergen avoidance counseling is effective for children with non-atopic asthma as well as atopic asthma.

New insights in allergen avoidance measures for mite and pet sensitized patients. A critical appraisal

It is widely acknowledged that avoidance of allergens such as those derived from foods, drugs, latex and stinging insects results in a complete disappearance of symptoms. By contrast, although it has been clearly shown that allergens are an important risk factor for the development of respiratory symptoms and that several avoidance measures reduce allergen levels, whether this gives clinical improvement in symptoms is debatable. Many reasons could be invoked to justify this evident discrepancy. Apart from the intrinsic methodological aspects (e.g. single or combined interventions measure, population studied, severity of respiratory symptoms, outcomes, evaluated parameters, etc.), it is important to outline that a successful approach requires that the avoided allergen is the only and real factor responsible for symptoms, the patient's education and the use of a comprehensive protocol to reduce allergen exposure. Other important factors include the involvement of the patient, the relevance of other allergens/non-specific agents, and exposure to sensitizing agents also outside patient's home. It is likely that the clinical phase of allergic airway disease and the degree of bronchial (and also nasal) remodelling, in each individual, represent relevant factors for the clinical outcome of allergen avoidance procedures. Since the management of respiratory allergy is a complex strategy (including drugs, allergen avoidance, immunological and educational interventions), it is difficult in real life to distinguish the efficacy of a single intervention in comparison to the others. A combined strategy is likely to produce better clinical results.

Encasement of bedding does not improve asthma in atopic adult asthmatics

AIM

We evaluated the impact of impermeable bed covers on asthma in asthmatics with clinically relevant house dust mite (HDM) sensitization.

METHODS

The study included 32 HDM-sensitized asthmatics in whom HDM allergy was considered as a significant factor in their asthma. They were randomized into either an intervention group whose bedding was encased with impermeable covers, or a control group who received cotton covers. Before and 3 and 6 months after encasement, dust samples were collected from the bedding and assayed for Der p 1. Clinical outcomes included quality of life, lung function, bronchial reactivity to methacholine, symptoms, medications and peak flow rates.

RESULTS

Baseline Der p 1 levels in both the active and the placebo groups were comparable and high (19.2 vs 18.9 microg/g of dust). There was a significant reduction in Der p 1 levels in the active group after 6 months, but not in the placebo group (7.3 vs 21.9 microg/g of dust). Quality of life improved significantly in both the intervention and control groups, but there was no significant difference in the improvements between the groups. There was no significant change in lung function, symptoms, and requirements for medications.

CONCLUSIONS

Encasement of bedding significantly reduced the Der p 1 levels. However, this was not sufficient to produce worthwhile clinical improvement in those in whom dust mite avoidance might well have been recommended as part of their clinical management.

Possible reasons for lack of effect of allergen avoidance in atopy-prone infants and sensitive asthmatic patients

The basic paradigm that allergen exposure produces atopic sensitization, and that continued exposure leads to clinical asthma throughout the development of airway inflammation and bronchial hyperreactivity has been challenged. However, because it was observed that epidemiological evidence suggests that around 40% of asthma cases are attributable to atopy (even using restrictive criteria), the obvious corollary is that if allergen avoidance begins before the onset of sensitization (primary prevention), then it should be associated with a reduced number of new cases of the disease. However, there are conflicting results regarding the effect of allergen avoidance on primary prevention of atopic sensitization and asthma onset. Instead, more uniform and positive results are available from secondary prevention studies. Secondary prevention obviously is an attractive opportunity for pediatricians who may recognize the patients who might benefit from these interventions simply by screening for food allergy in young children with atopic dermatitis. The conflicting results of tertiary prevention are most frequently observed in adult patients and sometimes result from incomplete avoidance of allergens responsible for the sensitization.

High allergen exposure as a risk factor for asthma and allergic disease

The association between pet ownership in childhood and subsequent asthma and sensitization is very controversial. Intriguing, but contradictory, reports have caused considerable uncertainty in parents who wish to avoid asthma and allergic disease in their children. This article argues that high allergen exposure is a risk factor for asthma and allergic disease. It describes dispersal of pet allergens in society and critically assesses epidemiological studies regarding how early exposure to pet allergens affects subsequent immunoglobulin E-sensitization and allergic diseases. Additionally, this article evaluates the effects of allergen exposure in already sensitized subjects with asthma. Cat and dog allergens are ubiquitous in society and may induce sensitization and allergic symptoms in predisposed individuals, regardless of pet ownership. This, in combination with selection mechanisms for pet ownership in families with a history of allergic diseases, makes it difficult to study associations between early exposure to pets and subsequent allergic disease. Nevertheless, exposure to pet allergens worsens asthma in already sensitized children. Thus, it is clear that clinicians should advise sensitized asthmatics that avoidance of exposure to indoor allergens is an important element in the treatment of allergic disease.

The role of allergen avoidance in the secondary prevention of atopic disorders

PURPOSE OF REVIEW

Allergen avoidance is recommended as part of the treatment programme of many patients with allergic diseases in Europe and the USA. However, clinical trials of allergen avoidance tend to be small and the findings inconsistent. Several larger studies have recently been published, making a review of the new literature timely.

RECENT FINDINGS

There have been two large double-blind, placebo-controlled studies on the use of encasings (mattress, pillow and duvet) as a single intervention in adults with asthma. In both studies, participants in the active and the control group showed an improvement in peak flow, but there was no difference between groups over a 12-month period. A further smaller study of encasings reported an improvement in peak flow from 1 week in the active group; this study, however, was only of 9 weeks' duration. In children, the use of encasings was associated with a reduction in asthma medication usage, but not until 6 months into the study. A multifaceted intervention study, with the intervention tailored to the child's sensitization status and home environment (including environmental tobacco smoke), resulted in significant reductions in emergency room visits and symptoms in the active group.

SUMMARY

The evidence suggests that interventions in children (either single or multifaceted) are associated with a meaningful and sustained improvement in asthma control. However, for adults, allergen proof encasings as a single intervention cannot be recommended. There is a need for a large-scale multifaceted intervention study in adults with asthma.

Effect of mite-impermeable mattress encasings and an educational package on the development of allergies in a multinational randomized, controlled birth-cohort study -- 24 months results of the Study of Prevention of Allergy in Children in Europe

BACKGROUND

Sensitization to house dust mite (HDM) is an important risk factor for the development of asthma and allergic disease in childhood. Higher levels of HDM allergen are linked to increased sensitization to HDM.

OBJECTIVE

To study the effect of mite-impermeable mattress encasings and an educational package on the development of allergies in a newborn cohort.

METHODS

Six hundred and ninety-six newborns at high risk of developing allergies were enrolled in three European countries (Germany, Austria, UK) in a prospective, randomized, controlled birth-cohort study. Children were randomly assigned to an intervention and control group. Intervention measures included the use of mite-impermeable mattress encasings for the child's bed and a simple educational package on allergen avoidance. The control group received basic information about allergies. Children were followed up at age 6, 12, 18 and 24 months.

RESULTS

80.9% of the children were followed up to the age of 24 months. No difference in the prevalence of sensitization to HDM (control vs. intervention group: 8.4% vs. 6.1%, P=0.33) or the development of symptoms (recurrent wheezing 10.3% vs. 10.7%, nocturnal cough 12.5% vs. 12.5%) or allergic diseases (asthma 3.5% vs. 5.1%, eczema 20.0% vs. 19.6%, rhinitis 28.9% vs. 25.8%) could be found between the control and intervention group.

CONCLUSION

In this study, HDM avoidance did not show a protective effect on the development of sensitization to HDM or symptomatic allergy in children at age 24 months.

Allergen avoidance and prevention of atopy

PURPOSE OF REVIEW

Recent increases in the prevalence of atopic disease argue strongly that environmental factors operating primarily in early life play a significant role. Exposure to food and inhalant allergens early in life may constitute a risk factor amenable to manipulation.

RECENT FINDINGS

Recent observational and interventional studies have produced conflicting data regarding the effectiveness of allergen avoidance in primary and secondary prevention of atopic diseases.

SUMMARY

Exclusive breast feeding for 4-6 months may protect against the development of allergic diseases in early childhood and remains good advice. Convincing proof for the preventive effects of the delayed introduction of solid foods and hydrolyzed formula in formula-fed infants is lacking. There is some evidence to support a preventive effect of house dust mite allergen avoidance before sensitization occurs. The effect of exposure to animal allergen is uncertain, with some studies showing an increase in sensitization while others suggest a protective effect. Therefore, no evidence-based advice can be given at this stage regarding allergen avoidance measures to be adopted by families with infants at high risk of atopy, except perhaps to breast feed exclusively for at least 4 months. Data regarding the secondary prevention of allergic disease by allergen avoidance were more secure until the publication this year of two randomized controlled trials which suggest that mattress impermeable covers, the main dust mite allergen avoidance measure, may not work. Allergen avoidance, however, should remain an essential part of the management of allergic diseases, even if the benefit of mattress covers is in doubt.

House dust mite control measures for asthma

BACKGROUND

The major allergen in house dust comes from mites. Chemical, physical and combined methods of reducing mite allergen levels are intended to reduce asthma symptoms in people who are sensitive to house dust mites.

OBJECTIVES

To assess the effects of reducing exposure to house dust mite antigens in the homes of people with mite-sensitive asthma.

SEARCH STRATEGY

Cochrane Airways Group trials register, and PubMed and The Cochrane Library (last searches June 2004), reference lists.

SELECTION CRITERIA

Randomised trials of mite control measures vs placebo or no treatment in asthmatic people known to be sensitive to house dust mites.

DATA COLLECTION AND ANALYSIS

Two reviewers applied the trial inclusion criteria, assessed their quality and extracted the data independently. Study authors were contacted to clarify information.

MAIN RESULTS

Forty-nine trials (2733 patients) were included; the number of patients has more than doubled since the last version of this review. Thirty-one trials assessed physical methods, ten assessed chemical methods, and eight a combination of chemical and physical methods. Despite the fact that many trials were of poor quality and would be expected to exaggerate the reported effect, we did not find an effect of the interventions. For the most frequently reported outcome, peak flow in the morning (1339 patients), the standardised mean difference was -0.02 (95% confidence interval (CI) -0.13 to 0.08). There were no statistically significant differences either in number of patients improved (relative risk 1.01, 95% CI 0.80 to 1.27), asthma symptom scores (standardised mean difference -0.01, 95% CI -0.10 to 0.13), or in medication usage (standardised mean difference -0.05, 95% CI -0.18 to 0.09).

REVIEWERS' CONCLUSIONS

Chemical and physical methods aimed at reducing exposure to house dust mite allergens cannot be recommended. It is doubtful whether further studies, similar to the ones in our meta-analysis, are worthwhile. If other types of studies are considered, they should be methodologically rigorous and use other methods than those used so far, with careful monitoring of mite exposure and relevant clinical outcomes.

Human leucocyte antigen polymorphisms in nut-allergic patients in South Wales

BACKGROUND

Peanuts and tree nuts are among the most common foods provoking severe allergic reactions including fatal anaphylaxis. However, little is known of the underlying genetic and immunological mechanisms involved.

OBJECTIVE

Based on findings in other allergic diseases, we have investigated whether specific human leucocyte antigens (HLA) are associated with nut allergy.

METHOD

Eighty-four patients presenting at the allergy clinic with symptoms of nut allergy were typed for the HLA Class I (HLA-A and B) and Class II (HLA-DRB1 and DQB1) loci by PCR using sequence-specific primers. Carriage frequencies were compared with 82 atopic non-nut-allergic subjects and 1798 random blood donors.

RESULTS

The frequency of HLA-B(*)07 (28.57%) and DRB1(*)11 (15.48%) was increased in the nut-allergic patients compared to the atopic controls (12.20% and 3.66%, respectively) but not when compared to the blood donors (28.86% and 10.12%). DRB1(*)13 and DQB1(*)06 were both increased in frequency in the nut allergy patients over both the atopic and blood donor controls. However, none of these increased frequencies were significant when corrected for the number of comparisons undertaken.

CONCLUSION

At HLA '2-digit resolution' and with undifferentiated patients with nut allergy, there are no major disturbances in the frequency of HLA-A, B, DRB1 or DQB1 types. However, the difference in frequency of HLA-DRB1(*)11 between the nut allergy patients and the atopic controls merits further investigation as this may represent an important phenotypic relationship.

A review of the effects of impermeable bedding encasements on dust-mite allergen exposure and bronchial hyper-responsiveness in dust-mite-sensitized patients

BACKGROUND

Sensitization and exposure to dust-mite antigens are causative factors in the development and exacerbation of asthma. Impermeable bedding encasements are considered a first-line treatment to reduce dust-mite antigen exposure in clinical asthma-management guidelines. Public-health recommendations for environmental asthma treatments should be based on the weight of evidence supporting the reliability of environmental interventions so that uncertainties regarding their effectiveness can be accurately communicated to patients, and so that limited public-health resources can be most effectively utilized.

OBJECTIVE

To evaluate the strength of a clinical-trial evidence supporting the efficacy of bedding encasements as an asthma treatment.

METHODS

A narrative review was conducted of all clinical trials involving bedding encasement for the treatment of asthma. Collective statistical analyses were also performed to characterize the quantitative effect of bedding encasement on dust-mite allergen exposure and bronchial hyper-responsiveness (BHR) when used by asthma patients.

RESULTS

Over 30 clinical trials were reviewed. Of those studies reporting adequate exposure and BHR results, four reported significant reduction in dust-mite allergen exposure and concomitant BHR reduction in active-treatment groups using bedding encasements. In 10 studies, mite-allergen exposure was reportedly decreased during the study, but BHR was not changed in the active-treatment group or was reduced to a similar degree in the active-treatment and control groups. Five other studies reported a lack of significant effect of the intervention on exposure and BHR. Collective paired analyses found that the effect of bedding encasement on allergen exposure and BHR tended toward only a modest, non-significant improvement. Collectively, effects of bedding encasement on BHR and dust-mite allergen exposure were modestly correlated only when the baseline exposure was above 2 microg Type 1 antigen per gram settled dust.

CONCLUSION

Although bedding encasement might be an effective asthma treatment under some conditions, when implemented in clinical trials by asthma patients, its effectiveness is inconsistent and appears to be, at best, modest. Therefore, its significance as a reliable asthma management modality for any individual asthma patient is uncertain. Where resource constraints are significant, targeting the use of variably effective interventions such as bedding encasements toward those patient sub-populations most likely to derive substantial benefit may gain the largest net public-health benefit.

Control of exposure to mite allergen and allergen-impermeable bed covers for adults with asthma

BACKGROUND

The effectiveness of avoidance of house-dust-mite allergen (Dermatophagoides pteronyssinus 1 [Der p1]) in the management of asthma is uncertain.

METHODS

We conducted a double-blind, randomized, placebo-controlled study of allergen-impermeable bed covers involving 1122 adults with asthma. The primary outcomes were the mean morning peak expiratory flow rate over a four-week period during the run-in phase and at six months and the proportion of patients who discontinued inhaled corticosteroid therapy as part of a phased-reduction program during months 7 through 12. Der p1 was measured in mattress dust in a 10 percent random subsample of homes at entry and at 6 and 12 months.

RESULTS

The prevalence of sensitivity to dust-mite allergen was 65.4 percent in the group supplied with allergen-impermeable bed covers (active-intervention group) and 65.1 percent in the control group supplied with non-impermeable bed covers. The concentration of Der p1 in mattress dust was significantly lower in the active-intervention group at 6 months (geometric mean, 0.58 microg per gram vs. 1.71 microg per gram in the control group; P=0.01) but not at 12 months (1.05 microg per gram vs. 1.64 microg per gram; P=0.74). The mean morning peak expiratory flow rate improved significantly in both groups (from 410.7 to 419.1 liters per minute in the active-intervention group, P<0.001 for the change; and from 417.8 to 427.4 liters per minute in the control group, P<0.001 for the change). After adjustment for base-line differences (by analysis of covariance), there was no significant difference between the groups in the peak expiratory flow rate at six months (difference in means, active-intervention group vs. control group, -1.6 liters per minute [95 percent confidence interval, -5.9 to 2.7] among all patients [P=0.46] and -1.5 liters per minute [95 percent confidence interval, -6.9 to 3.9] among mite-sensitive patients [P=0.59]). There was no significant difference between the groups in the proportion in whom complete cessation of inhaled corticosteroid therapy was achieved (17.4 percent in the active-intervention group and 17.1 percent in the control group) or in the mean reduction in steroid dose, either among all patients or among mite-sensitive patients.

CONCLUSIONS

Allergen-impermeable covers, as a single intervention for the avoidance of exposure to dust-mite allergen, seem clinically ineffective in adults with asthma.