Impact of Short-Term Exposure to Below Recommended PM10 Pollution Levels on Asthma Exacerbations.

Air pollution significantly affects health, causing up to 7 million premature deaths annually and generating an even larger number of hospitalizations and days of sick leave [1]. The negative impact of pollutants on human health is well known. Several epidemiological studies have reported positive associations between exposure to particulate matter (PM) and morbidity and mortality associated with obstructive pulmonary diseases, including asthma [2-3]. Although there is well-documented evidence that short-term exposures to PM10, ozone, and NO2 contribute to asthma exacerbations [4], no threshold for PM10 concentrations has been established below the maximum recommended by World Health Organization (WHO) [5]. This study aims to analyze whether levels and duration of exposure to PM10 can have an impact on asthmatic patients who visit the emergency department (ED) with an asthma exacerbation. We conducted a retrospective, observational cohort-study using data collected at the ED of Hospital Universitario La Paz, Madrid, Spain from January 1 to December 31, 2014. The hospital is a tertiary referral center serving a population of 500 000 in northern Madrid. The search procedure, enrolment, and data collection have been addressed elsewhere [6]. The study population comprised 831 patients aged >14 years, who attended the ED with an asthma exacerbation. For each event, data were collected on 84 variables—considering patient characteristics in terms of epidemiology and comorbid conditions—according to the consensus criteria of the 2009 Spanish guideline on asthma management (GEMA 2009) [7]. The study was approved by the local ethics committee, and permission was obtained for the use of confidential data. Hourly PM10 concentrations collected from 3 different stations (Cuatro Caminos, Paseo de la Castellana, and Plaza de Castilla) in the hospital catchment area were retrieved from the institutional database of Madrid City Council between December 28, 2013 and December 31, 2014 [8]. Hourly PM10 data were measured using a heated tapered element oscillating microbalance. Average hourly concentrations were calculated using the hourly concentration of the referred measurement stations. We limited data to PM10 concentrations of between 10 μg/m3 and 40 μg/m3 and exposure times from 4 hours to 16 hours, in 2-hour intervals, with a 2-day lag to each individual ED visit. A total of 11 025 models were examined to validate the procedure, considering different PM10 levels and duration of exposure for each patient. Significance was set at 95%. The parameters of the models were evaluated using both maximum likelihood estimators and a bootstrap approach (50 replications); both models yielded the same results (Supplementary Figure 2). The association between PM10 levels, exposure times, and asthma episodes was studied using a logistic regression model for binary outcomes and both continuous and binary independent variables. The independent variables were age, sex, and a binary variable that explains the level of exposure to PM10 pollutants for a 2-day lag prior to the ED visit. The initial data processing to build the model was performed using MATLAB-R2020, while the models were developed using STATA-V24. The outcome of the analysis was the probability of an exacerbation in asthmatic patients who visited the ED. According to the model results (Figure), if there is a PM10 concentration of 22 μg/m3 for a 10-hour period the day prior to the ED visit and a PM10 level of between 14 μg/m3 and 30 μg/ m3 for a 10-hour period 2 days prior to the visit (see blue line), there is a moderate probability of an asthma exacerbation (0.18-0.26, P<.05). When the PM10 concentration and exposure time are increased (38 μg/m3 for 16 hours the day prior to the ED visit and a PM10 level between 26 μg/m3 and 30 μg/m3 for 16 hours 2 days prior to the ED visit), the probability of an asthma exacerbation rises to 48%. In the real world, dynamic changes in air pollutants and meteorological factors coexist [9]. Age, temperature, allergen concentrations, and various pollutants play a role in increasing or decreasing the risk of an asthma exacerbation [10], although it remains unclear how PM10 affects this risk. A recent metaanalysis concluded that an increase of 10 μg/m3 in acute PM10 exposure was associated with a change of –0.19 L/min