Single interventions to reduce indoor allergens typically do not improve asthma outcomes, but multicomponent interventions do show some success, according to a systematic review published in The Journal of Allergy and Clinical Immunology.
The review was conducted as part of an update to the National Heart, Lung, and Blood Institute (NHLBI) clinical practice guidelines for asthma.
The research team was led by Brian F. Leas, MS, MA, of the University of Pennsylvania Health System, Philadelphia, PA. They searched other systematic reviews, randomized controlled trials, and nonrandomized interventional studies. In all, 59 randomized and 8 non-randomized trials involving 8 interventions were included. Single component interventions were covered in 39 of the studies, and 30 studies assessed multicomponent interventions.
Primary outcomes of the review included validated measures of asthma controls, such as the Asthma Control Questionnaire (ACQ) or Asthma Control Test (ACT), asthma-related exacerbations, healthcare utilization and costs, pulmonary physiology, and quality of life.
A summary of the findings for select interventions is below.
Seven of the included studies involved a single intervention of an application of acaricides on mattresses, carpets, and upholstery for the eradication of house dust mite allergens. No improvements in pulmonary physiology were reported vs placebo or other interventions.
Multicomponent interventions, including acaricides, were investigated in six studies, but no improvements in pulmonary physiology or asthma symptoms were found.
As a single intervention, the evidence for air purification as a method of asthma control was inconclusive; no difference was observed for exacerbations or pulmonary physiology measures.
One study did find that Asthma Quality of Life Questionnaire (AQLQ) scores improved with air purification, while two other studies found no effect on quality of life.
In the five studies in which researchers evaluated air purification as part of a multicomponent intervention, school absenteeism decreased, asthma symptoms improved, and allergen levels were reduced. However, there was no reported improvement in asthma control, exacerbations, or quality of life.
High-efficiency particulate air (HEPA) vacuum filters
The use of a HEPA vacuum as part of a multicomponent strategy showed improved asthma symptoms in children, but not among mixed populations of children, adolescents, and adults. In addition, quality of life improved in children younger than 12 years of age.
There was insufficient evidence to support improvements in asthma control and pulmonary physiology, but exacerbations were reduced.
Results of 14 studies of impermeable mattress covers showed no differences in asthma control, exacerbations, use of inhaled corticosteroids, rescue medications, pulmonary physiology, quality of life, or self-reported asthma symptoms. However, levels of dust mite allergens were reduced.
As part of a multicomponent approach, school absenteeism and missed activities decreased, but no improvements in other outcomes were noted.
Pest control strategies alone resulted in an improvement in self-reported asthma symptoms, but there was insufficient evidence that other outcomes were improved.
For the multicomponent studies, exacerbations were reduced, school absenteeism decreased, quality of life among children improved, asthma symptoms improved, and allergen levels were reduced for some pests. In contrast, no effects were seen on emergency department visits or hospitalizations, and the evidence was inconclusive for asthma control, medication use, and pulmonary physiology.
The findings in this review differed in several ways from the 2007 National Asthma Education and Prevention Program (NAEPP) guidelines and the clinical practice parameters of the American Academy of Allergy, Asthma, and Immunology. Researchers found that evidence for most of the interventions was either insufficient or low, while in other guidelines, there was greater evidence for some benefits.
This review included many recent findings that showed no effect for the interventions, which may explain the discrepancy. In addition, researchers did not include the same studies that were included in other guidelines, due to differences in inclusion criteria.
There was also a high level of heterogeneity across the studies included. Variations in patient characteristics, asthma severity, and likelihood of patients experiencing a benefit from the interventions affected the results of the review when compared with prior reviews.
Home-based interventions are also notoriously difficult to implement properly because of costs, technology, types of homes, and health literacy. Some of the studies included in this review involved a specially-trained community health worker to help patients reduce home allergen exposure. The direct impact of these workers was not evaluated.
The authors wrote: “It is important for clinicians to consider the complexity of their patient population and the limitations of the evidence that we have identified. When recommending specific steps of action, clinicians may find it helpful to consider a patient’s individual sensitization and reaction to specific allergens, as well as the severity of the patient’s asthma and the extent of previous symptoms and exacerbations.”
To read more about this study, click here.
This project was supported by the Agency for Healthcare Research and Quality, US 42 Department of Health and Human Services.