Effect of ambient relative humidity and particulate matter on the levels of asthma therapy

Objective: We aimed to investigate the associations of the daily mean and short-term variation in ambient relative humidity (RH), temperature, and fine particulate matter (PM2.5) with asthma treatment steps. Methods: We consecutively recruited 288 newly diagnosed adult patients with asthma and followed them for at least 6 months according to the Global Initiative for Asthma (GINA) strategy. Odds ratios (ORs) for higher GINA treatment steps required to achieve asthma control were estimated using logistic regression. We also conducted exposure-response analyses to explore potentially nonlinear relationships between environmental exposure and asthma treatment step across seasons. Results: A 1% increase in the 1-day RH difference and a 1-μg/m3 increase in the 7-day PM2.5 difference were associated with 1.054-fold and 1.052-fold higher odds of step 4 treatment, respectively. A 1% increase in the 1-day RH difference and a 1-μg/m3 increase in the 7-day PM2.5 difference were associated with 1.047-fold and 1.056-fold higher odds of medium-dose inhaled corticosteroids plus long-acting beta-agonists (ICS + LABA), respectively. A 1% increase in the 7-day RH mean and a 1-μg/m3 increase in the 30-day PM2.5 difference were associated with 1.075-fold and 1.205-fold higher odds of triple inhaler therapy and biologics use, respectively. Exposure-response analyses suggested noticeable seasonal patterns for temperature and RH in relation to asthma treatment strategy. Conclusions: Our exploratory and hypothesis-generating findings showed that greater short-term variation in RH and PM2.5 was associated with higher treatment intensity in adult asthma, particularly the use of medium-dose ICS + LABA and biologics. Higher RH mean was also associated with triple inhaler therapy. These associations were more evident during the cold season. Multicenter validation studies in larger population studies are warranted.