Asthma is a common disease with a lifetime prevalence of approximately 20 percent. The management of asthma includes anti-inflammatory and bronchodilator medications. Recently, concern has been raised about the effect of environmental influences, such as indoor and outdoor air quality, on asthma control. One method of controlling indoor air quality is to use high-efficiency particulate air filter systems. These systems have been shown to reduce both large and small particulate matter in the air, and in one study reduced the level of cat allergens. However, current recommendations do not include these systems as an option in asthma treatment because of insufficient data. McDonald and colleagues performed a systematic review of the evidence from randomized trials that evaluated the effectiveness of residential air filtration systems on patients with asthma.

The authors reviewed all of the randomized trials they could identify through MEDLINE, the Cumulative Index to Nursing and Allied Health Literature, and the Cochrane Collaboration Controlled Trials Registry. They reviewed the references cited in the various studies, and they contacted authorities in the area of study, as well as air filtration manufacturers. The authors identified 10 relevant randomized trials that studied the impact of air filtration systems on asthma symptoms. They abstracted data from the various trials, including methodologic quality, study population, intervention, and outcomes.

Five of the studies enrolled adults only, while one of the studies involved only children. The total population for all of the studies combined was 216 patients with an established diagnosis of asthma. Participants who received air filtration systems had significantly lower scores in total symptoms and sleep disturbance, but the heterogeneity of the results weakened the ability to draw a conclusion based on these trials. The air filtration systems had no impact on medication use or morning peak expiratory flow values. None of the studies reviewed used any validated quality-of-life measurements.

The authors conclude that air filtration systems are associated with fewer symptoms but have no impact on medication use or morning peak flow measurements. They add that rigorous randomized trials should be performed to determine if these systems have any positive impact on quality of life and symptom control in patients with asthma.