International Journal of Environmental Research and Public Health Article Long-Term Exposure to PM2.5, Facemask Mandates, Stay Home Orders and COVID-19 Incidence in the United States Fang Fang 1, Lina Mu 2, Yifang Zhu 3,4, Jianyu Rao 1,5, Jody Heymann 6 and Zuo-Feng Zhang 1,7,8,* 1 Department of Epidemiology, Fielding School of Public Health, University of California at Los Angeles (UCLA), Los Angeles, CA 90095, USA; [email protected] (F.F.); [email protected] (J.R.) 2 Department of Epidemiology and Environmental Health, School of Public Health and Health Professions, University at Buffalo, The State University of New York, Buffalo, NY 14214, USA; [email protected] 3 Department of Environmental Health Science, University of California at Los Angeles (UCLA), Los Angeles, CA 90095, USA; [email protected] 4 Institute of the Environment and Sustainability, University of California at Los Angeles (UCLA), Los Angeles, CA 90095, USA 5 Department of Pathology and Laboratory Medicine, David Geffen School of Medicine, University of California at Los Angeles (UCLA), Los Angeles, CA 90095, USA 6 WORLD Policy Analysis Center, University of California at Los Angeles (UCLA), Los Angeles, CA 90095, USA; [email protected] 7 Jonsson Comprehensive Cancer Center, University of California at Los Angeles (UCLA), Los Angeles, CA 90095, USA 8 Center for Human Nutrition, Department of Medicine, David Geffen School of Medicine, University of California at Los Angeles (UCLA), Los Angeles, CA 90095, USA * Correspondence: [email protected] Abstract: Long-term PM2.5 exposure might predispose populations to SARS-CoV-2 infection and Citation: Fang, F.; Mu, L.; Zhu, Y.; intervention policies might interrupt SARS-CoV-2 transmission and reduce the risk of COVID-19. We Rao, J.; Heymann, J.; Zhang, Z.-F. conducted an ecologic study across the United States, using county-level COVID-19 incidence up to Long-Term Exposure to PM2.5, 12 September 2020, to represent the first two surges in the U.S., annual average of PM2.5 between Facemask Mandates, Stay Home 2000 and 2016 and state-level facemask mandates and stay home orders. We fit negative binomial Orders and COVID-19 Incidence in the United States. Int. J. Environ. Res. models to assess COVID-19 incidence in association with PM2.5 and policies. Stratified analyses 3 Public Health 2021, 18, 6274. https:// by facemask policy and stay home policy were also performed. Each 1-µg/m increase in annual doi.org/10.3390/ijerph18126274 average concentration of PM2.5 exposure was associated with 7.56% (95% CI: 3.76%, 11.49%) increase in COVID-19 risk. Facemask mandates and stay home policies were inversely associated with Academic Editors: David Carpenter COVID-19 with adjusted RRs of 0.8466 (95% CI: 0.7598, 0.9432) and 0.9193 (95% CI: 0.8021, 1.0537), and Paul B. Tchounwou respectively. The associations between PM2.5 and COVID-19 were consistent among counties with or without preventive policies. Our study added evidence that long-term PM2.5 exposure increased Received: 10 April 2021 the risk of COVID-19 during each surge and cumulatively as of 12 September 2020, in the United Accepted: 5 June 2021 States. Although both state-level implementation of facemask mandates and stay home orders were Published: 10 June 2021 effective in preventing the spread of COVID-19, no clear effect modification was observed regarding long-term exposure to PM2.5 on the risk of COVID-19. Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in Keywords: particulate matter; COVID-19; facemasks; stay-home orders; nation-wide study published maps and institutional affil- iations. 1. Introduction A novel coronavirus disease (COVID-19) was first discovered in Wuhan, China in Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. December 2019 [1], and on 11 March 2020, a global pandemic was declared by the World This article is an open access article Health Organization (WHO) [2]. As of 12 September 2020, COVID-19 has infected 6,353,677 distributed under the terms and people in the United States [3]. To avoid the human-to-human transmission of the pathogen, conditions of the Creative Commons the U.S. Centers for Disease Control and Prevention (CDC) recommends social distanc- Attribution (CC BY) license (https:// ing, face masking, and good hygiene practices [4]. Each state also implements different creativecommons.org/licenses/by/ policies in order to slow down the spread of the disease [5]. A meta-analysis including 4.0/). 21 studies showed the efficacy of face masks in preventing respiratory virus transmission. Int. J. Environ. Res. Public Health 2021, 18, 6274. https://doi.org/10.3390/ijerph18126274 https://www.mdpi.com/journal/ijerph Int. J. Environ. Res. Public Health 2021, 18, 6274 2 of 12 The protective effect of facemask use against respiratory virus infection was 64% and a 47% risk reduction was observed among non-healthcare workers. Among the studies included, one study observed a 96% reduction of COVID-19 risk among Chinese healthcare workers using facemasks [6]. A recent study also demonstrated face coverings as effective preventive measures in slowing down the viral transmission via droplets by mimicking cough-generated airborne particles in an indoor environment. The study showed that surgi- cal and K95/KN95 masks reduced cough droplets dramatically [7]. By utilizing COVID-19 cases from 190 countries between 23 January 2020, and 13 April 2020, non-pharmaceutical interventions, such as mandatory masks, quarantine, distancing and traffic restriction, were inversely associated with the reproduction number of COVID-19. The reductions in repro- duction numbers were −15.14% (from −21.79% to −7.93%) for mandatory facemask and −42.94% (from −44.24% to −41.60%) for distancing. When two or more interventions were implemented simultaneously, a greater decrease in the reproduction number of COVID-19 was observed [8]. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was identified as the definitive infectious agent; however, social and environmental factors, such as air pollution, may also play a contributory role in the transmission of the virus in human population [9]. Fine particulate matter (particles with aerodynamic diameter equal to or less than 2.5 µm in diameter, PM2.5) may affect disease via a variety of mechanisms such as altering immune response, increasing oxidative stress, causing inflammatory injury, inducing mutagenicity and introducing respiratory tract damage [10–12]. Moreover, ambient air pollution was associated with various infectious outcomes, such as deaths due to lower respiratory infection [13], elevated fatality of severe acute respiratory syndrome (SARS) in China [14], increased risk of influenza [15], and upper respiratory infections incidence and hospital admission for respiratory infections [16]. In addition, SARS-CoV-2 can remain viable in aerosols for hours [17] and air particles are suspected to be capable of carrying the virus and facilitating its spread [18]. Table1 summarizes current literature on the association between air pollution and COVID-19 outcomes. Studies in Northern Italy and among cities in China reported positive correlations between short-term exposure to PM2.5 and COVID-19 outcomes [19–23]. A Korean study concluded temporal association between COVID-19 incidence and other air pollutants, but not with PM2.5 [24]. Exposure to long-term PM2.5 was associated with COVID-19 mortality after controlling for different confounders [25–30]. In the United States, 3 Wu et al. showed that each 1-µg/m increase in long-term PM2.5 exposure (2000–2016 annual average) was associated with 11% increase in COVID-19 mortality [25], which was also affected by the presence of other hazardous air pollutants [26]. Hendryx et al. showed a positive association between long-term PM2.5 and COVID-19 prevalence and fatality as of 31 May 2020, by applying a linear regression model [30]. Timely evidence on the association between long-term exposure to air pollution, especially PM2.5, and COVID-19 incidence is accumulating in the United States and in Europe based on arbitrary cutoff points of the pandemic. With the progression of COVID-19, more extensive data would allow us to examine whether COVID-19 incidence was associated with long-term exposure to PM2.5 during each surge of the pandemic and whether it might be modified by the implementation of preventive interventions, such as facemask mandates or stay home policies. Int. J. Environ. Res. Public Health 2021, 18, 6274 3 of 12 Table 1. Literature Review on Air Pollution and COVID-19. Study Area Study Period Statistical Model Findings 3 Daily PM10 exceeding 50 µg/m with a Northern Italy [19] 24 February 2020– Recursive binary partitioning 15-day lag was a significant predictor for 13 March 2020 tree approach COVID-19 incidence Daily PM2.5 was positively associated with COVID-19 incidence with RR from Poison regression adjusting 1.036 to 1.144. The association with Chinese cities (Wuhan, 25 January 2020– for other air pollutants and PM10 was negative with RR between Xiaogan and Huanggang) [20] 29 February 2020 meteorological variables in 0.915 and 0.964. Results for other each city pollutants (SO2, CO, NO2, and 8-hour O3) were not consistent among the study sites. PM2.5 and NO2 were positively Chinese cities (Wuhan and associated with COVID-19 incidence 26 January 2020– Univariate linear regression Xiaogan) [21] 29 February 2020 4 days later in both cities, while PM10 and CO were inconsistent between cities. PM2.5, PM10, NO2 and O3 with a 2-week lag were positively associated with Generalized additive model COVID-19 incidence, while SO2 was 120 Chinese cities [22] 23 January 2020– adjusting for meteorological negatively associated. A 10µg/m3 29 February 2020 variables with city fixed effects increase in PM2.5 with a 2-week lag was associated with a 2.24% increase in COVID-19 incidence.