title: Effect of air filtration systems on asthma: a systematic review of randomized trials.
abstract: OBJECTIVE
  To systematically review the evidence of randomized trials evaluating the effects of residential air filtration systems on patients with asthma.
  
  
  METHODS
  We searched for published and unpublished studies using MEDLINE, the Cumulative Index to Nursing and Allied Health Literature, and the Cochrane Collaboration. We reviewed all reference lists for additional articles of relevance, and contacted experts in the field and air filter manufacturers.
  
  
  METHODS
  We identified 10 relevant randomized controlled trials that examined the influence of a residential air filtration system on patients with asthma.
  
  
  METHODS
  In duplicate and independently, we abstracted data on the methodologic quality, population, intervention, and outcomes.
  
  
  RESULTS
  Five of 10 studies enrolled adults only. One study included children only. The sample size ranged from 9 to 45 participants in each study, for a total of 216 patients across all studies. Two studies reported a statistically significant decrease in airway responsiveness associated with air filter utilization. Air filters were associated with significantly lower total symptom scores (weighted mean difference of 0.47; 95% confidence interval [CI], 0.69 to 0.25) on a 10-point scale, and lower sleep disturbance score (weighted mean difference of 0.93; 95% CI, 1.44 to 0.42); however, heterogeneity of results weakens the inferences from these trials. Air filtration systems were not associated with any differences in medication use or morning peak expiratory flow values. None of these trials employed validated scales to measure clinical symptoms or quality of life.
  
  
  CONCLUSIONS
  Among patients with allergies and asthma, use of air filters is associated with fewer symptoms. Rigorous sufficiently powered randomized clinical trials are needed to more precisely define the influence of air filtration on health-related quality of life and symptom control for asthmatic patients.
authors.affiliation: Departments of Clinical Epidemiology and Biostatistics, McMaster University, Hamilton, ON, Canada. emcdonal@mcmaster.ca
authors.forename: Ellen
authors.initials: E
authors.lastname: McDonald
authors.forename: Deborah
authors.initials: D
authors.lastname: Cook
authors.forename: Toni
authors.initials: T
authors.lastname: Newman
authors.forename: Lauren
authors.initials: L
authors.lastname: Griffith
authors.forename: Gerard
authors.initials: G
authors.lastname: Cox
authors.forename: Gordon
authors.initials: G
authors.lastname: Guyatt
mesh_terms: D000389:Air Conditioning; D001249:Asthma / Q000517:prevention & control*; D005374:Filtration; D006801:Humans; D016032:Randomized Controlled Trials as Topic