Wildfire-Specific PM2.5 is Associated with Mental Health and Pregnancy-Related Outcomes During the 2020 California Fires

Background: Studies of the 2020 wildfires in California have been based on limited geographic areas and found inconsistent health-related outcomes. Additionally, the impact of wildfires on mental health and pregnancy is understudied.Methods: A population-based ecological study was conducted among people presenting to hospitals in California from July 1 to December 31, 2020.Using a distributed non-linear lagged model, we investigated the immediate (day 0) and delayed (up to 4 days) associations between 10 ug/m3 increases in wildfire-specific PM2.5 and emergency department (ED) visits due to potentially PM2.5-related diseases (respiratory, cardiovascular, mental, and pregnancy-related) after adjusting for COVID-19 co-occurrence.Findings: A 10 ug/m3 increase in wildfire-specific PM2.5 concentration per over 4 lag days was associated with an increase in the number of ED visits for chronic lower respiratory conditions (cumulative relative risk (cRR) =1.121 [95% CI 1.071-1.174]), asthma (cRR 1.154 [1.090-1.222]), and all respiratory conditions (cRR 1.026 [1.001-1.052]). Various exposure windows showed significant increases in COPD (lag 0-3: 1.126 [0.949-1.336]), combined mental conditions (lag 0-2: 1.052 [1.017-1.089]), other mood affective disorders (lag 0-3: 1.189 [1.035-1.364]), and all pregnancy-related conditions (lag 0-4: 1.035 [1.001-1.071]). Subgroup analyses indicated that Medicaid enrollees, females, and adults (age 25-64) had higher risks for ED visits during wildfires. Mediation analyses showed that the percent excess risk of wildfire-specific PM2.5 on outcomes explained by COVID-19 was -7% for respiratory and -31% for pregnancy-related.Conclusions: We found significant associations of wildfire smoke exposure and ED visits for mental and pregnancy-related outcomes. We also confirmed previously reported associations with respiratory and cardiovascular outcomes. Each health outcome had different lag times of susceptibility to wildfire smoke exposure and varied by sociodemographic characteristics, including age, sex, race/ethnicity, and health insurance types.Funding: This study was supported by the grants from the National Institutes of Health (NIH) AIRHEALTH P01 HL152953 and the Sean N Parker Center for Allergy and Asthma Research at Stanford University.Declaration of Interest: All authors declare no competing interests.