Effectiveness of the Air Purification Strategies for the Treatment of Allergic Asthma: A Meta-Analysis.

We updated the meta-analysis published by McDonald et al. [Chest 2002;122;1535-1542] by reviewing the effectiveness of air purification for the treatment of home-related allergic asthma (dust mite, dog, cat, and cockroach). We analysed the trials included by McDonald et al. as well as studies published since 2000. Data on asthma symptoms scores (ASS), medication use, forced expiratory volume in 1 s as a percentage of the predicted value (FEV1 %pred), histamine provocative concentration causing a 20% reduction in FEV1 (PC20), Asthma Quality of Life Questionnaire (AQLQ) scores, and fractional exhaled nitric oxide (FeNO) levels were extracted. The effectiveness was examined using metafor (registered in Prospero CRD42019127227). Ten trials including a total of 482 patients (baseline characteristics: mean FEV1 %pred 83.2%, I2 = 96.7%; mean PC20 4.93 mg/mL, I2 = 44.0%; mean AQLQ 4.67 [max. 7], I2 = 93.7%; mean FeNO 36.5 ppb, I2 = 0%) were included. We assessed the mean differences in the AQLQ scores as +0.36 (95% CI 0.10 to 0.62, p = 0.01, n = 302, I2 = 0%) and the FeNO levels as -6.67 ppb (95% CI -10.56 to -2.77, p = 0.0008, n = 304, I2 = 0%). The standardised mean differences in all other health outcomes were not significant (ASS -0.68, p = 0.20; medication use: -0.01, p = 0.94; FEV1 %pred -0.11, p = 0.34; PC20 +0.24, p = 0.53). We found statistically significant mean differences in the AQLQ scores and FeNO levels in patients with predominantly mild to moderate asthma at baseline. A large trial reported great improvement in the subgroup of patients receiving Global Initiative for Asthma step 4 therapy. We recommend that future studies on air purification focus on patients with severe and poorly controlled allergic asthma.