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BACKGROUND: 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. OBJECTIVE: We examined individual-level associations between six criteria air pollutants and influenza using case- crossover design. METHODS: 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 (P[M.sub.2.5] and P[M.sub.10]), sulfur dioxide (S[O.sub.2]), nitrogen dioxide (N[O.sub.2]), ozone ([O.sub.3]) 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. RESULTS: N = 108,479 eligible cases were identified in our study. Every 10- [micro]g/[m.sup.3] increase in exposure to P[M.sub.2.5], P[M.sub.10], N[O.sub.2], and CO and every 5-[micro]g/[m.sup.3] increase in S[O.sub.2] 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 [O.sub.3] and influenza with a RR of 0.878 (95% CI: 0.866, 0.890). CONCLUSIONS: Our findings suggest that short-term exposure to air pollution, except for [O.sub.3], is associated with greater risk for influenza. Further studies are necessary to decipher underlying mechanisms and design preventive interventions and policies. https://doi.org/10.1289/EHP12145, Introduction Influenza is an infectious disease of the respiratory tract caused by human influenza viruses, contributing to global mortality and morbidity, as well as to the related economic burden. An [...]

BACKGROUND: Although residing in lower surrounding greenness and transient exposure to air pollution are independently associated with higher risk of adverse health outcomes, little is known about their interactions. OBJECTIVES: We examine whether residential neighborhood greenness modifies the short-term association between air pollution and respiratory mortality among the participants of Chinese Elderly Health Service Cohort in Hong Kong. METHODS: We estimated residential surrounding greenness by measuring satellite-derived normalized difference vegetation index (NDVI) from Landsat within catchments of residential addresses of participants who died of respiratory diseases between 1998 and 2011. We first dichotomized NDVI into low and high greenness and used a time-stratified case-crossover approach to estimate the percent excess risk of respiratory mortality associated with fine particulate matter (PM2.5), respirable particulate matter (PM10), nitrogen dioxide (NO2), and ozone (O3). We further classified NDVI into greenness quartiles and introduced an interaction term between air pollution and the assigned median values of the NDVI quartiles into the models to assess the trend of greenness modification on the air pollution and respiratory mortality associations. RESULTS: Among 3159 respiratory deaths during the follow-up, 2058 were from pneumonia and 947 from chronic obstructive pulmonary disease. Elders living in the low greenness areas were associated with a higher risk of pneumonia mortality attributed to NO2 (p = 0.049) and O3 (p = 0.025). The mortality risk of pneumonia showed a decreasing trend for NO2 (p for trend = 0.041), O3 (p for trend = 0.006), and PM2.5 (p for trend = 0.034) with greenness quartiles increasing from Quartile 1 (lowest) to Quartile 4 (highest). CONCLUSIONS: Our findings suggest that elders living in higher greenness areas are less susceptible to pneumonia mortality associated with air pollution, which provides evidence for optimizing allocation, siting, and quality of urban green space to minimize detrimental health effects of air pollution.