Smoke and COVID-19 case fatality ratios during California wildfires

Abstract

Background: Recent evidence has shown an association between wildfire smoke and COVID-19 cases and deaths. The San Francisco Bay Area, in California (USA), experienced two major concurrent public health threats in 2020: the COVID-19 pandemic and dense smoke emitted by wildfires. This provides a unprecedented context to unravel the role of acute air pollution exposure on COVID-19 severity. Methods: A smoke product provided by the National Oceanic and Atmospheric Association Hazard Mapping System was used to identify counties exposed to heavy smoke in summer and fall of 2020. Daily COVID-19 cases and deaths for the United States were downloaded at the county-level from the CDC COVID Data Tracker. Synthetic control methods were used to estimate the causal effect of the wildfire smoke on daily COVID-19 case fatality ratios, adjusting for population mobility. Results: Evidence of an impact of wildfire smoke on COVID-19 case fatality ratios was observed, with precise estimates in Alameda and San Francisco. Up to 58 (95% CI: 29, 87) additional deaths for every 1,000 COVID-19 incident daily cases attributable to wildfire smoke was estimated in Alameda in early September. Conclusions: Findings indicated that extreme weather events such as wildfires smoke can drive increased vulnerability to infectious diseases, highlighting the need to further study these colliding crises. Understanding the environmental drivers of COVID-19 mortality can be used to protect vulnerable populations from these potentially concomitant public health threats.

The COVID-19-wildfire smoke paradox: Reduced risk of all-cause mortality due to wildfire smoke in Colorado during the first year of the COVID-19 pandemic

“…Our study contributes to the growing body of literature examining the concurrent effects of wildfire events and the COVID-19 pandemic on public health. Overall, air pollution related to WFS events is linked to greater COVID-19 infection and mortality ( Curtis, 2021 ; Schwarz et al, 2022 ; Zhou et al, 2021 ; Kiser et al, 2021 ). In Orange County, California, wildfire-related PM 2.5 exposures during a late wildfire season (fall of 2020) were associated with increases in COVID-19 infection rates ( Leifer et al, 2021 ).…”

“…Previous studies have investigated associations between WFS and COVID-19 mortality ( Curtis, 2021 ; Naqvi et al, 2022 ; Schwarz et al, 2022 ), but important gaps remain in our understanding of the interaction between COVID-19 and WFS on other causes of death. Examining WFS-related mortality before and during the pandemic will facilitate important comparisons between periods when behaviors and exposures may have differed substantially and allow us to assess whether individuals were dying from causes previously linked to WFS exposure during the pandemic.…”

Livestock removal increases plant cover across a heterogeneous dryland landscape on the Colorado Plateau

“…Synthetic control econometric studies generally quantify ratios or differences between treatments and controls at the scale of US counties or even entire countries (e.g. Mao 2018, Schwarz et al 2022. We instead analyze individual pixels and used the CE as a covariate in a multilevel model, which generated new insights into the influence of CE.…”

Sixth Oregon climate assessment

“…Influenza was associated positively with increasing PM 2.5 levels during wildfire season (Landguth et al 2020) (Table 4). Additionally, several studies have reported initial evidence of associations between exposure to wildfire smoke and SARS-CoV-2 infections (Curtis et al 2021, Leifer et al 2021, Meo et al 2021, Schwarz et al 2022) and deaths (Curtis 2021. For a comprehensive review of the impact of wildfire smoke on respiratory health, refer to Grant et al (2022).…”