Clinical effects of allergen avoidance

A review on human health perspective of air pollution with respect to allergies and asthma

The increase in cases of asthma and allergies has become an important health issue throughout the globe. Although these ailments were not common diseases a few short decades ago, they are now affecting a large part of the population in many regions. Exposure to environmental (both outdoor and indoor) pollutants may partially account for the prevalence of such diseases. In this review, we provide a multidisciplinary review based on the most up-to-date survey of literature regarding various types of airborne pollutants and their associations with asthma-allergies. The major pollutants in this respect include both chemical (nitrogen dioxide, ozone, sulfur dioxide, particulate matter, and volatile organic compounds) and biophysical parameters (dust mites, pet allergens, and mold). The analysis was extended further to describe the development of these afflictions in the human body and the subsequent impact on health. This publication is organized to offer an overview on the current state of research regarding the significance of air pollution and its linkage with allergy and asthma.

Respiratory health in home and leisure pursuits

Many home-based and leisure activities can generate hazardous respirable exposures. Routine domestic activities and a variety of hobbies, avocations, and leisure pursuits have been associated with a spectrum of respiratory tract disorders. Indoor environments present a special risk for high-intensity exposures and adverse health effects. There are important knowledge gaps regarding the prevalence of specific health hazards within and across communities, exposure-response effects, population and individual susceptibilities, best management strategies, the adverse health effects of mixed exposures, and long-term clinical outcomes following exposures. The home environment presents special health risks that should be part of the health assessment.

Mono and multifaceted inhalant and/or food allergen reduction interventions for preventing asthma in children at high risk of developing asthma

BACKGROUND

Allergen exposure is one of the environmental factors seemingly associated with the development of asthma. If asthma is a multi-factorial disease, it is hypothesised that prevention might only prove effective if most or all relevant environmental factors are simultaneously avoided.

OBJECTIVES

To assess effect(s) of monofaceted and multifaceted interventions compared with control interventions in preventing asthma and asthma symptoms in high risk children.

SEARCH STRATEGY

We searched the Cochrane Airways Trials Register (December 2008).

SELECTION CRITERIA

Randomised controlled trials of allergen exposure reduction for the primary prevention of asthma in children. Interventions were multifaceted (reducing exposure to both inhalant and food allergens) or monofaceted (reducing exposure to either inhalant or food allergens) Follow up had to be from birth (or during pregnancy) up to a minimum of two years of age.

DATA COLLECTION AND ANALYSIS

We included in the analysis studies assessing the primary outcome (current diagnosis: asthma) and/or one of the secondary outcomes (current respiratory symptoms: wheezing, nocturnal coughing and dyspnoea). We pooled multifaceted and monofaceted intervention trials separately. We made an indirect comparison of their effects using tests for interaction to calculate relative odds ratios.

MAIN RESULTS

We included three multifaceted and six monofaceted intervention studies (3271 children). Physician diagnosed asthma in children less than five years, and asthma as defined by respiratory symptoms and lung function criteria in children aged five years and older, both favoured treatment with a multifaceted intervention compared to usual care (< 5 years: odds ratio (OR) 0.72, 95% confidence interval (CI) 0.54 to 0.96, and > 5 years: OR 0.52, 95% CI 0.32 to 0.85). However, there was no significant difference in outcome between monofaceted intervention and control interventions (< 5 years: OR 1.12, 95% CI 0.76 to 1.64, and > 5 years: OR 0.83, 95% CI 0.59 to 1.16). Indirect comparison between these treatments did not demonstrate a significant difference between multiple interventions and mono-interventions in reducing the frequency of asthma diagnosis in children under five years (relative OR 0.64 (95% CI 0.40 to 1.04, P = 0.07) or five years and older (relative OR 0.63, 95% CI 0.35 to 1.13, P = 0.12). There was also no significant difference between either mono- and multifaceted intervention and control in reducing the likelihood of symptoms of nocturnal coughing at follow up. Wheezing, however, showed a significant difference between multifaceted and mono-interventions (relative OR 0.59, 95% CI 0.35 to 0.99, P = 0.04), but the significance was lost when data on treatment only was analysed.

AUTHORS' CONCLUSIONS

The available evidence suggests that the reduction of exposure to multiple allergens compared to usual care reduces the likelihood of a current diagnosis of asthma in children (at ages < 5 years and 5 years and older). Mono-intervention studies have not produced effects which are statistically significant compared with control. In children who are at risk of developing childhood asthma, multifaceted interventions, characterised by dietary allergen reduction and environmental remediation, reduce the odds of a physician diagnosis of asthma later in childhood by half. This translates to a number needed to treat (NNT) of 17. The effect of multi-faceted interventions on parent reported wheeze was inconsistent and had no significant impact on nocturnal coughing or dyspnoea. Data from monofaceted intervention exposed children studies were not significantly different from those of control groups for all outcomes. There remains uncertainty as to whether multiple interventions are more effective than mono-component interventions. The comparisons made were indirect, making the conclusions drawn uncertain. To our knowledge there are no ongoing studies in which both intervention strategies are randomly compared. The findings, however, warrant further direct comparison between multiple- and monofaceted interventions aimed at reducing the prevalence of asthma in children.

Environmental allergens and asthma morbidity in low-income children

Asthma morbidity is high in inner-city children in the United States, which may be related in part to increased allergens in poorly maintained housing. This study examined asthma morbidity in relation to mold, cockroach, dust mite, and cat allergens in the homes of 61 low-income Chicago children with asthma. Children exposed to higher levels of Penicillium in the bedroom had more frequent asthma symptoms, whereas those exposed to higher levels of cockroach allergen in the bedroom had a higher number of asthma symptoms. Respiratory infections confounded the association of cockroach allergen with number of asthma symptoms.

How is the indoor environment related to asthma?: literature review

AIMS

This paper reports a review conducted to identify the factors in the indoor environment that have an evidence-based link with the exacerbation or development of asthma and to identify measures that healthcare professionals can promote to reduce exposure to these risk factors in the home.

BACKGROUND

The indoor environment, particularly at home, has been recognized as a major source of exposure to allergens and toxic chemicals. Exposure to allergens and toxins is thought to exacerbate respiratory conditions, in particular, asthma.

METHODS

Searches were made of health and indoor environment databases, including Cochrane Library, National Health Services Centre for Reviews and Assessment Reports, British Medical Journal, CINAHL and Ovid library, MEDSCAPE/MEDLINE, EMBASE, INGENTA, Science Citation Index, Web of Science. Searches were also made of other Internet-based resources, including those of international and government bodies. The following keywords were used: allergens, allergen avoidance, asthma, asthma prevention, cat, damp, Der p 1, dog, environmental control, house dust mites, indoor air quality, indoor environment, meta analysis, mould, pets, remedial actions, respiratory illnesses and systematic reviews.

FINDINGS

There is evidence of a link between asthma and a small number of indoor environmental factors. There is currently only reasonable evidence for one causative factor for asthma in the indoor environment and that is house dust mite allergen. Although there are many studies of different remedial actions that can be taken in the home, often these give evidence of reduced risk of exposure but not clinical improvement in asthma. Although there is a lack of medical evidence for the reduction of known sensitizers such as mould, this is because of a dearth of research rather than evidence of no association.

CONCLUSIONS

There is some evidence of a link between the indoor environment and asthma. There are measures, which could be promoted by healthcare professionals to alleviate asthmatic symptoms.

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

BACKGROUND

House dust mite (HDM) allergy is a frequent cause of allergic asthma in children. Reduction of exposure seems to be the most logical way to treat these patients.

OBJECTIVE

Our aim was to investigate whether mattress and pillow encasings resulted in an effective long-term control of HDM allergen levels, thereby reducing the need for asthma medication in children with asthma and HDM allergy.

METHODS

In a prospective, double-blind, placebo-controlled study 60 children (age range, 6-15 years) with asthma and HDM allergy were randomized to active (allergy control) or placebo mattress and pillow encasings. After a 2-week baseline period, follow-up was performed every 3 months for 1 year. During the entire study period, the dose of inhaled steroids was tapered off to the lowest effective dose according to well-defined criteria.

RESULTS

Fifty-two patients completed the trial, and 5 were excluded, leaving data from 47 children (26 in the active treatment group and 21 in the placebo group) for analysis. A significant perennial reduction in HDM allergen concentrations was seen only for the active treatment group. Also, a significant decrease in the dose of inhaled steroids (mean, 408 to 227 microg/d; P <.001) was found for the active treatment group only, with significant differences between groups after 9 and 12 months. After 1 year, the dose of inhaled steroids was reduced by at least 50% in significantly more children in the active treatment group than in the placebo group (73% vs 24%, P <.01).

CONCLUSION

Encasing of mattresses and pillows resulted in a significant long-term reduction in HDM allergen concentrations in mattresses and in the need for inhaled steroids in children with asthma and HDM allergy.

Environmental controls in the management of allergic asthma

Environmental allergen control is one of the four primary goals of good asthma management. The American Academy of Allergy, Asthma, and Immunology has published a position statement [78] that endorses the National Asthma Education and Prevention Program management guidelines [23] and recommends that every patient with persistent asthma be evaluated for environmental allergen sensitivity. Patients who have sensitivities should receive practical advice on allergen avoidance. An accumulating body of knowledge indicates that such measures, when strictly applied for a sufficient period of time, can indeed reduce asthma symptoms, need for medication, and airway hyperresponsiveness. Ongoing prospective trials in large numbers of patients are being conducted and should enhance the ability to make proper recommendations to patients.