Prenatal exposure to wildfire-related PM2.5 and respiratory infections by age 1 year: A population-based case-control analysis of critical developmental windows

Background The 2017 and 2018 wildfire seasons in British Columbia (BC), Canada were unprecedented. Among all the pollutants in wildfire smoke, fine particulate matter (PM2.5) poses the most significant risk to human health. There is limited research on prenatal wildfire-related PM2.5 exposure and its impacts on infant health. Objectives We assessed the effect of prenatal wildfire-related PM2.5 exposure on respiratory infections in the first year of life. We explored exposure windows based on prenatal respiratory tract development and gestational trimester. Methods All live singleton infants in utero during the wildfire seasons (July to September) from 2016 to 2019 were identified using the BC Perinatal Data Registry (BCPDR). The Canadian Optimized Statistical Smoke Exposure Model (CanOSSEM) was used to estimate daily PM2.5 exposures throughout pregnancy and the first year of life. Infants who were diagnosed with otitis media or a lower respiratory infection by age 1 year were identified, including infections associated with dispensations of the antibiotic amoxicillin. The odds ratios (OR) for exposures during specific developmental windows and gestational trimesters were estimated with logistic regression, conditioned on epidemiologic week of birth to control for seasonal trends. Analyses were adjusted for multiple environmental and individual-level covariates. Results There were 134,475 infants included in the cohort, of which 22,093 were diagnosed with at least one outcome of interest. For every 10 μg/m3 increase in wildfire-related PM2.5, the OR [95% confidence interval] for otitis media associated with the fourth window of eustachian tube development (weeks 19-28) was 1.08 [1.02, 1.16]. Results were similar for infections associated with amoxicillin dispensations and during the second trimester (weeks 14-27) of development. Similarly, the canalicular stage of lower respiratory tract development (weeks 18-27) and the second trimester were associated with increased odds of lower respiratory tract infections. Conclusion Specific windows of prenatal exposure to wildfire-related PM2.5 during the second trimester were associated with increased odds of otitis media and lower respiratory infections by age 1 year. Study questions Is prenatal exposure to wildfire-related PM2.5 associated with risk of respiratory infections in the first year of life? If so, what are the critical prenatal exposure windows? What’s already known Few studies have focused on prenatal exposure to wildfire-related PM2.5 and respiratory outcomes in the very early stages of life, nor the critical windows for gestational exposures. Evidence suggests that wildfire-related PM2.5 may impact the foetus directly or indirectly, potentially leading to adverse consequences for foetal respiratory tract development and vulnerability of the respiratory system in early life. What this study adds Prenatal exposure to wildfire-related PM2.5 during specific periods of respiratory tract development were associated with increased risk of otitis media and lower respiratory infections by age 1 year. Results were similar for all infections and those associated with antibiotic dispensations. This study suggests that wildfire-related PM2.5 exposure during specific developmental windows can affect respiratory health in early life. Public health practitioners and healthcare providers should work to protect pregnant people and their children from the detrimental effects of wildfire smoke. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement This study was funded by Canadian Institutes of Health Research Grant (CIHR). ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: This work received approval from the UBC Research Ethics Board (Certificate number: H20-01077) and Population Data BC (approval number: 20-197). I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes Access to data provided by the Data Stewards is subject to approval but can be requested for research projects through the Data Stewards or their designated service providers. All inferences, opinions, and conclusions drawn in this publication are those of the author(s), and do not reflect the opinions or policies of the Data Stewards (the British Columbia Ministry of Health, the Perinatal Services BC).