Associations between Short-Term Exposure to Ambient Air Pollution and Influenza: An Individual-Level Case-Crossover Study in Guangzhou, China

Abstract

<h3>Background:</h3><p>Influenza imposes a heavy burden on public health. Little is known, however, of the associations between detailed measures of exposure to ambient air pollution and influenza at an individual level.</p><h3>Objective:</h3><p>We examined individual-level associations between six criteria air pollutants and influenza using case-crossover design.</p><h3>Methods:</h3><p>In this individual-level time-stratified case-crossover study, we linked influenza cases collected by the Guangzhou Center for Disease Control and Prevention from 1 January 2013 to 31 December 2019 with individual residence-level exposure to particulate matter (PM_2.5 and PM₁₀), sulfur dioxide (SO₂), nitrogen dioxide (NO₂), ozone (O₃) and carbon monoxide (CO). The exposures were estimated for the day of onset of influenza symptoms (lag 0), 1–7 d before the onset (lags 1–7), as well as an 8-d moving average (lag07), using a random forest model and linked to study participants’ home addresses. Conditional logistic regression was developed to investigate the associations between short-term exposure to air pollution and influenza, adjusting for mean temperature, relative humidity, public holidays, population mobility, and community influenza susceptibility</p><h3>Results:</h3><p><em>N</em> <em>= </em>108,479 eligible cases were identified in our study. Every 10-μg/m³increase in exposure to PM_2.5, PM₁₀, NO₂, and CO and every 5-μg/m³ increase in SO₂ over 8-d moving average (lag07) was associated with higher risk of influenza with a relative risk (RR) of 1.028 (95% CI: 1.018, 1.038), 1.041 (95% CI: 1.032, 1.049), 1.169 (95% CI: 1.151, 1.188), 1.004 (95% CI: 1.003, 1.006), and 1.134 (95% CI: 1.107, 1.163), respectively. There was a negative association between O₃and influenza with a RR of 0.878 (95% CI: 0.866, 0.890).</p><h3>Conclusions:</h3><p>Our findings suggest that short-term exposure to air pollution, except for O₃, is associated with greater risk for influenza. Further studies are necessary to decipher underlying mechanisms and design preventive interventions and policies.</p>