Bedroom air filter does not affect pollen allergy symptoms

Reference

Li L, Zhan L, Mo J-H, et al. Efficacy of indoor air purification in the treatment of Artemisia pollen-allergic rhinitis: A randomised, double-blind, clinical controlled trial. Clin Otolaryngol 2020;45(3):394-401.

Synopsis

Artemisia is the most common cause of allergic rhinitis in China and is also found commonly on other continents beyond Asia. This study, conducted in China during the pollen season, enrolled 90 patients with documented sensitivity to Artemisia pollen. On a scale from 1 to 7, with higher scores signifying greater symptoms, the initial score was an average 2.4 in the enrollees. The patients were randomized (allocation concealment uncertain) to receive an air purifier with either a HEPA (Atmosphere air purifier, $1770 US) or placebo filter, with instructions to place it in the bedroom and have it run continuously for 4 weeks. Participants did not take allergy medicines for the duration of the study unless they experienced a steep decline in their sleep quality or in their quality of work or daily life (the number of patients who did so was not reported). Over the course of 4 weeks, symptom severity increased similarly in both the filter and placebo groups (from an average 2.4 to 3.5 and 3.7, respectively), possibly because the patients were not allowed to take their normal allergy medication. However, scores on the Rhinoconjunctivitis Quality of Life Questionnaire improved similarly in both groups. The only outcome significantly improved with the purifier was an allergy symptom score comprising eye- and nose-related symptoms. Scores were also improved on the Epworth Sleepiness Scale, which is normally used to evaluate patients with obstructive sleep apnea. This study fails to have several safeguards in place to avoid bias, and the statistics the authors used have me scratching my head in confusion.