Dust mite control measures don’t help asthma patients

ILLUSTRATIVE CASE

The parents of a 10-year-old patient whom you recently diagnosed with asthma want to do everything they can to reduce his asthma symptoms. They are considering buying hypoallergenic mattress covers and an expensive air filtration system to decrease the levels of dust mite allergens in their home and want to know if you think that will help their son. What do you tell them?

We want to do everything we can to help our patients control their asthma symptoms, but when it comes to household dust mite control measures, this extensive Cochrane review confirms that interventions like mattress covers and air filtration don’t work, despite recent reviews and guidelines recommending them.

Dust mites (Dermatophagoides pteronyssinus) are one of the most common allergens that provoke asthma symptoms in children and adults.² Dust mites live in warm, humid places and feed on human skin scales. The areas with the highest levels of household infestation are carpets, mattresses, pillows, drapes, upholstered furniture, and clothing.

Guidelines still encourage mattress cover use

The National Asthma Education and Prevention Program (NAEPP) 2007 guidelines recommend using allergen-impermeable mattress and pillow covers and washing sheets and blankets in hot water. They also recommend “considering” reducing indoor humidity, removing bedroom carpets, and washing stuffed toys weekly. The NAEPP Expert Panel cites many studies to support these recommendations.³

The National Environmental Education and Training Foundation (NEETF) 2005 guidelines recommend additional measures to reduce dust mite exposure including vacuuming using a high-efficiency particulate air (HEPA) filter, removing draperies, and considering using a portable air cleaner with a HEPA filter.⁴

STUDY SUMMARY: 54 trials, but no support for dust mite measures

This Cochrane systematic review included 54 randomized trials that assessed the effects of physical and/or chemical interventions to reduce exposure to house dust mite antigens in the homes of patients with mite-sensitive asthma. These studies included a total of 3002 pediatric and adult asthma patients (9 - 628 patients analyzed per trial) with mite sensitization confirmed by skin testing or IgE serum assays.

Thirty-six studies tested physical interventions, including mattress covers, vacuum cleaning, heating, ventilation, freezing, washing, air filtration, and ionizers. Ten used chemical interventions to kill dust mites; 8 used a combination of physical and chemical methods. Control groups received either placebo or no treatment.

Outcomes studied. The authors extracted data for the following outcomes: subjective well-being, asthma symptom scores, use of medication, days of sick leave from school or work, number of unscheduled visits to a physician or hospital, forced expiratory volume in 1 second (FEV₁), peak expiratory flow rate (PEFR), and provocative concentration that causes a 20% fall in FEV₁ (PC20). Length of the intervention and follow-up ranged from 2 weeks to 2 years.

Quality of studies. According to modern standards for randomized trials, the quality of many of the 54 studies was not optimal, especially in the descriptions of randomization and the reporting of outcomes. The method of randomization and concealment of allocation was rarely described. Eleven trial reports did not contain any usable data for the meta-analysis because of the way data were reported, and there was significant potential for reporting bias in favor of a treatment effect in the studies included. Mite reduction was successful in 17 trials, unsuccessful in 24 trials, and not reported in 13 trials.

Interventions didn’t help. There were no differences between the intervention and control groups for any of the outcomes. The percentage of patients who improved after the experimental interventions was not significantly different from the percentage of patients in the control groups (relative risk [RR]=1.01; 95% confidence interval [CI], 0.80-1.27; data based on 7 trials). There was no difference in medication usage (data from 10 trials), FEV₁ (data from 14 trials), morning PEFR (data from 23 trials), or PC 20 (data from 14 trials) between the intervention and control groups ( TABLE ).¹

TABLE
Dust mite control measures didn’t improve these outcomes

WHAT’S NEW?: Nothing is new, yet this will be “news” to many

This Cochrane review includes 5 additional trials that have been conducted since the last Cochrane review of this topic in 2004. However, the 2004 review reported the same conclusion—that interventions to reduce house dust mite exposure in asthma patients are ineffective—as did 3 other Cochrane reviews on the same topic beginning in 1998.^5-8

So why are the guidelines out of step? Schmidt and Gøtzsche (one of the authors of the Cochrane review) conducted a systematic review of narrative review articles in 2005 to answer this question. They found 70 review articles, 90% of which recommended physical methods to reduce exposure to house dust mites. They discovered that although these review articles included references to support their recommendations of dust mite control measures, the reviews showed significant bias in favor of positive studies and highlighted the results of low-quality studies, including non-randomized studies that had been excluded from the Cochrane reviews.⁹

CAVEATS: Duration of studies not long enough?

We know that extreme measures to reduce exposure to dust mite allergen, such as relocating to a high altitude or prolonged hospitalization, can reduce asthma symptoms,^10,11 but these are clearly not practical solutions for most patients with dust mite-sensitive asthma. When it comes to this Cochrane review, some might argue that many of the interventions included were not of sufficient duration and did not sufficiently reduce the level of house mite allergen to improve asthma symptoms.

However, the subgroups of trials with long treatment duration (1-2 years) and successful mite reduction (determined by different methods, including mite counts and measured antigen levels in dust samples) also failed to show a significant difference between intervention and control groups.¹

Tweak the approach? Most dust mite-sensitive asthma patients are sensitive to other allergens, so perhaps multifaceted interventions that target multiple allergens would be more effective.¹² But until these potential interventions are supported by stronger evidence, we should not recommend them to our patients.

CHALLENGES TO IMPLEMENTATION: Swimming against the tide is never easy

Although the evidence to date indicates that interventions to reduce home dust mite exposure are ineffective, there are hundreds of products—including mattress and pillow covers ($10-$100), ionizers ($100-$200), and air filtration systems ($500-$800)—that are being marketed to patients with asthma. In addition, patient education handouts from sources such as the American Academy of Family Physicians, the American Academy of Pediatrics, and UpToDate recommend implementing dust mite control measures to reduce dust mite allergen exposure.^13-15

We need to start educating our asthma patients properly so they can spend their time, energy, and money on interventions, such as medications, that work—and not on interventions that make no difference.

Acknowledgements

The PURLs Surveillance System is supported in part by Grant Number UL1RR024999 from the National Center for Research Resources, a Clinical Translational Science Award to the University of Chicago. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Center for Research Resources or the National Institutes of Health.

This study was selected and evaluated using FPIN’s Priority Updates from the Research Literature (PURL) Surveillance System methodology. The criteria and findings leading to the selection of this study as a PURL can be accessed at www.jfponline.com/purls.

ILLUSTRATIVE CASE

The parents of a 10-year-old patient whom you recently diagnosed with asthma want to do everything they can to reduce his asthma symptoms. They are considering buying hypoallergenic mattress covers and an expensive air filtration system to decrease the levels of dust mite allergens in their home and want to know if you think that will help their son. What do you tell them?

We want to do everything we can to help our patients control their asthma symptoms, but when it comes to household dust mite control measures, this extensive Cochrane review confirms that interventions like mattress covers and air filtration don’t work, despite recent reviews and guidelines recommending them.

Dust mites (Dermatophagoides pteronyssinus) are one of the most common allergens that provoke asthma symptoms in children and adults.² Dust mites live in warm, humid places and feed on human skin scales. The areas with the highest levels of household infestation are carpets, mattresses, pillows, drapes, upholstered furniture, and clothing.

Guidelines still encourage mattress cover use

The National Asthma Education and Prevention Program (NAEPP) 2007 guidelines recommend using allergen-impermeable mattress and pillow covers and washing sheets and blankets in hot water. They also recommend “considering” reducing indoor humidity, removing bedroom carpets, and washing stuffed toys weekly. The NAEPP Expert Panel cites many studies to support these recommendations.³

The National Environmental Education and Training Foundation (NEETF) 2005 guidelines recommend additional measures to reduce dust mite exposure including vacuuming using a high-efficiency particulate air (HEPA) filter, removing draperies, and considering using a portable air cleaner with a HEPA filter.⁴

STUDY SUMMARY: 54 trials, but no support for dust mite measures

This Cochrane systematic review included 54 randomized trials that assessed the effects of physical and/or chemical interventions to reduce exposure to house dust mite antigens in the homes of patients with mite-sensitive asthma. These studies included a total of 3002 pediatric and adult asthma patients (9 - 628 patients analyzed per trial) with mite sensitization confirmed by skin testing or IgE serum assays.

Thirty-six studies tested physical interventions, including mattress covers, vacuum cleaning, heating, ventilation, freezing, washing, air filtration, and ionizers. Ten used chemical interventions to kill dust mites; 8 used a combination of physical and chemical methods. Control groups received either placebo or no treatment.

Outcomes studied. The authors extracted data for the following outcomes: subjective well-being, asthma symptom scores, use of medication, days of sick leave from school or work, number of unscheduled visits to a physician or hospital, forced expiratory volume in 1 second (FEV₁), peak expiratory flow rate (PEFR), and provocative concentration that causes a 20% fall in FEV₁ (PC20). Length of the intervention and follow-up ranged from 2 weeks to 2 years.

Quality of studies. According to modern standards for randomized trials, the quality of many of the 54 studies was not optimal, especially in the descriptions of randomization and the reporting of outcomes. The method of randomization and concealment of allocation was rarely described. Eleven trial reports did not contain any usable data for the meta-analysis because of the way data were reported, and there was significant potential for reporting bias in favor of a treatment effect in the studies included. Mite reduction was successful in 17 trials, unsuccessful in 24 trials, and not reported in 13 trials.

Interventions didn’t help. There were no differences between the intervention and control groups for any of the outcomes. The percentage of patients who improved after the experimental interventions was not significantly different from the percentage of patients in the control groups (relative risk [RR]=1.01; 95% confidence interval [CI], 0.80-1.27; data based on 7 trials). There was no difference in medication usage (data from 10 trials), FEV₁ (data from 14 trials), morning PEFR (data from 23 trials), or PC 20 (data from 14 trials) between the intervention and control groups ( TABLE ).¹

TABLE
Dust mite control measures didn’t improve these outcomes

WHAT’S NEW?: Nothing is new, yet this will be “news” to many

This Cochrane review includes 5 additional trials that have been conducted since the last Cochrane review of this topic in 2004. However, the 2004 review reported the same conclusion—that interventions to reduce house dust mite exposure in asthma patients are ineffective—as did 3 other Cochrane reviews on the same topic beginning in 1998.^5-8

So why are the guidelines out of step? Schmidt and Gøtzsche (one of the authors of the Cochrane review) conducted a systematic review of narrative review articles in 2005 to answer this question. They found 70 review articles, 90% of which recommended physical methods to reduce exposure to house dust mites. They discovered that although these review articles included references to support their recommendations of dust mite control measures, the reviews showed significant bias in favor of positive studies and highlighted the results of low-quality studies, including non-randomized studies that had been excluded from the Cochrane reviews.⁹

CAVEATS: Duration of studies not long enough?

We know that extreme measures to reduce exposure to dust mite allergen, such as relocating to a high altitude or prolonged hospitalization, can reduce asthma symptoms,^10,11 but these are clearly not practical solutions for most patients with dust mite-sensitive asthma. When it comes to this Cochrane review, some might argue that many of the interventions included were not of sufficient duration and did not sufficiently reduce the level of house mite allergen to improve asthma symptoms.

However, the subgroups of trials with long treatment duration (1-2 years) and successful mite reduction (determined by different methods, including mite counts and measured antigen levels in dust samples) also failed to show a significant difference between intervention and control groups.¹

Tweak the approach? Most dust mite-sensitive asthma patients are sensitive to other allergens, so perhaps multifaceted interventions that target multiple allergens would be more effective.¹² But until these potential interventions are supported by stronger evidence, we should not recommend them to our patients.

CHALLENGES TO IMPLEMENTATION: Swimming against the tide is never easy

Although the evidence to date indicates that interventions to reduce home dust mite exposure are ineffective, there are hundreds of products—including mattress and pillow covers ($10-$100), ionizers ($100-$200), and air filtration systems ($500-$800)—that are being marketed to patients with asthma. In addition, patient education handouts from sources such as the American Academy of Family Physicians, the American Academy of Pediatrics, and UpToDate recommend implementing dust mite control measures to reduce dust mite allergen exposure.^13-15

We need to start educating our asthma patients properly so they can spend their time, energy, and money on interventions, such as medications, that work—and not on interventions that make no difference.

Acknowledgements

The PURLs Surveillance System is supported in part by Grant Number UL1RR024999 from the National Center for Research Resources, a Clinical Translational Science Award to the University of Chicago. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Center for Research Resources or the National Institutes of Health.

This study was selected and evaluated using FPIN’s Priority Updates from the Research Literature (PURL) Surveillance System methodology. The criteria and findings leading to the selection of this study as a PURL can be accessed at www.jfponline.com/purls.

ILLUSTRATIVE CASE

The parents of a 10-year-old patient whom you recently diagnosed with asthma want to do everything they can to reduce his asthma symptoms. They are considering buying hypoallergenic mattress covers and an expensive air filtration system to decrease the levels of dust mite allergens in their home and want to know if you think that will help their son. What do you tell them?

We want to do everything we can to help our patients control their asthma symptoms, but when it comes to household dust mite control measures, this extensive Cochrane review confirms that interventions like mattress covers and air filtration don’t work, despite recent reviews and guidelines recommending them.

Dust mites (Dermatophagoides pteronyssinus) are one of the most common allergens that provoke asthma symptoms in children and adults.² Dust mites live in warm, humid places and feed on human skin scales. The areas with the highest levels of household infestation are carpets, mattresses, pillows, drapes, upholstered furniture, and clothing.

Guidelines still encourage mattress cover use

The National Asthma Education and Prevention Program (NAEPP) 2007 guidelines recommend using allergen-impermeable mattress and pillow covers and washing sheets and blankets in hot water. They also recommend “considering” reducing indoor humidity, removing bedroom carpets, and washing stuffed toys weekly. The NAEPP Expert Panel cites many studies to support these recommendations.³

The National Environmental Education and Training Foundation (NEETF) 2005 guidelines recommend additional measures to reduce dust mite exposure including vacuuming using a high-efficiency particulate air (HEPA) filter, removing draperies, and considering using a portable air cleaner with a HEPA filter.⁴

STUDY SUMMARY: 54 trials, but no support for dust mite measures

This Cochrane systematic review included 54 randomized trials that assessed the effects of physical and/or chemical interventions to reduce exposure to house dust mite antigens in the homes of patients with mite-sensitive asthma. These studies included a total of 3002 pediatric and adult asthma patients (9 - 628 patients analyzed per trial) with mite sensitization confirmed by skin testing or IgE serum assays.

Thirty-six studies tested physical interventions, including mattress covers, vacuum cleaning, heating, ventilation, freezing, washing, air filtration, and ionizers. Ten used chemical interventions to kill dust mites; 8 used a combination of physical and chemical methods. Control groups received either placebo or no treatment.

Outcomes studied. The authors extracted data for the following outcomes: subjective well-being, asthma symptom scores, use of medication, days of sick leave from school or work, number of unscheduled visits to a physician or hospital, forced expiratory volume in 1 second (FEV₁), peak expiratory flow rate (PEFR), and provocative concentration that causes a 20% fall in FEV₁ (PC20). Length of the intervention and follow-up ranged from 2 weeks to 2 years.

Quality of studies. According to modern standards for randomized trials, the quality of many of the 54 studies was not optimal, especially in the descriptions of randomization and the reporting of outcomes. The method of randomization and concealment of allocation was rarely described. Eleven trial reports did not contain any usable data for the meta-analysis because of the way data were reported, and there was significant potential for reporting bias in favor of a treatment effect in the studies included. Mite reduction was successful in 17 trials, unsuccessful in 24 trials, and not reported in 13 trials.

Interventions didn’t help. There were no differences between the intervention and control groups for any of the outcomes. The percentage of patients who improved after the experimental interventions was not significantly different from the percentage of patients in the control groups (relative risk [RR]=1.01; 95% confidence interval [CI], 0.80-1.27; data based on 7 trials). There was no difference in medication usage (data from 10 trials), FEV₁ (data from 14 trials), morning PEFR (data from 23 trials), or PC 20 (data from 14 trials) between the intervention and control groups ( TABLE ).¹

TABLE
Dust mite control measures didn’t improve these outcomes

WHAT’S NEW?: Nothing is new, yet this will be “news” to many

This Cochrane review includes 5 additional trials that have been conducted since the last Cochrane review of this topic in 2004. However, the 2004 review reported the same conclusion—that interventions to reduce house dust mite exposure in asthma patients are ineffective—as did 3 other Cochrane reviews on the same topic beginning in 1998.^5-8

So why are the guidelines out of step? Schmidt and Gøtzsche (one of the authors of the Cochrane review) conducted a systematic review of narrative review articles in 2005 to answer this question. They found 70 review articles, 90% of which recommended physical methods to reduce exposure to house dust mites. They discovered that although these review articles included references to support their recommendations of dust mite control measures, the reviews showed significant bias in favor of positive studies and highlighted the results of low-quality studies, including non-randomized studies that had been excluded from the Cochrane reviews.⁹

CAVEATS: Duration of studies not long enough?

We know that extreme measures to reduce exposure to dust mite allergen, such as relocating to a high altitude or prolonged hospitalization, can reduce asthma symptoms,^10,11 but these are clearly not practical solutions for most patients with dust mite-sensitive asthma. When it comes to this Cochrane review, some might argue that many of the interventions included were not of sufficient duration and did not sufficiently reduce the level of house mite allergen to improve asthma symptoms.

However, the subgroups of trials with long treatment duration (1-2 years) and successful mite reduction (determined by different methods, including mite counts and measured antigen levels in dust samples) also failed to show a significant difference between intervention and control groups.¹

Tweak the approach? Most dust mite-sensitive asthma patients are sensitive to other allergens, so perhaps multifaceted interventions that target multiple allergens would be more effective.¹² But until these potential interventions are supported by stronger evidence, we should not recommend them to our patients.

CHALLENGES TO IMPLEMENTATION: Swimming against the tide is never easy

Although the evidence to date indicates that interventions to reduce home dust mite exposure are ineffective, there are hundreds of products—including mattress and pillow covers ($10-$100), ionizers ($100-$200), and air filtration systems ($500-$800)—that are being marketed to patients with asthma. In addition, patient education handouts from sources such as the American Academy of Family Physicians, the American Academy of Pediatrics, and UpToDate recommend implementing dust mite control measures to reduce dust mite allergen exposure.^13-15

We need to start educating our asthma patients properly so they can spend their time, energy, and money on interventions, such as medications, that work—and not on interventions that make no difference.

Acknowledgements

The PURLs Surveillance System is supported in part by Grant Number UL1RR024999 from the National Center for Research Resources, a Clinical Translational Science Award to the University of Chicago. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Center for Research Resources or the National Institutes of Health.

This study was selected and evaluated using FPIN’s Priority Updates from the Research Literature (PURL) Surveillance System methodology. The criteria and findings leading to the selection of this study as a PURL can be accessed at www.jfponline.com/purls.