Accounting for <i>in situ</i> air cleaner utilization and performance to improve interpretation of patient outcomes in real-world indoor air cleaner intervention trials

There is an increasing number of randomized clinical trials intended to assess the effectiveness of indoor air cleaners for improving participant outcomes in real-world settings. In this communication, we synthesize the current state of registered air cleaner intervention trials and call attention to the critical importance of conducting measurements to characterize the performance and <i>in situ</i> utilization of air cleaners in such trials to improve interpretation of exposure measurements and patient outcomes. We draw upon the existing literature and preliminary findings from our ongoing one-year, randomized, single-blind, placebo-controlled case-control trial of stand-alone air filtration in the homes of U.S. military Veterans to inform our recommendations. We demonstrate how to conduct industry-standard performance testing and how to use long-term measurements of air cleaner power draw to assess air cleaner operation. In our analysis of interim data from 53 homes to date with a mean data collection period of 275 days, we found that most air cleaners, whether active or sham, were operated predominantly at low or medium fan speeds, and most participants operated their air cleaner on predominantly one fan speed. In a few homes, air cleaners were mostly off. We estimate that air cleaner operation in these homes is providing a median additional equivalent particle loss rate of ∼0.7/h (ranging ∼0-2.8/h). Accordingly, we recommend that air cleaner intervention trials adopt the steps described herein to account for the amount of clean air delivered in real-world settings and to provide important context alongside indoor exposure measurements and analysis of patient outcomes.