Wildfire Seasons, Prenatal PM2.5 Exposure, and Respiratory Infections by Age 1 Year: A Population-Based Case-Control Analysis of Critical Developmental Windows

Abstract

The 2017 and 2018 wildfire seasons in British Columbia (BC), Canada were unprecedented. Among all the pollutants in wildfire smoke, fine particulate matter (PM_2.5) poses the most significant risk to human health. There is limited research on prenatal wildfire smoke exposure and its impacts on infant health. We used a population-based nested case-control design to assess the association between daily PM_2.5 exposures during specific developmental windows and the occurrence of otitis media or lower respiratory infections by age 1 year, including infections associated with dispensations of the antibiotic amoxicillin. We observed the strongest association between per 10 μg/m³ increase in PM_2.5 exposure and otitis media during the fourth window of eustachian tube development (weeks 19-28) with an OR [95% confidence interval] of 1.31 [1.22, 1.41]. Similarly, the canalicular stage of lower respiratory tract development (weeks 18-27) was associated with the highest odds of lower respiratory infections, with an OR of 1.21 [1.15, 1.28]. Measures to reduce wildfire smoke exposure during pregnancy are warranted.

Figure 1

Population of British Columbia by 2016 Census Divisions (panel A) and daily outdoor population-weighted average fine particulate matter (PM_2.5) concentrations during the study period (panel B). The dashed lines show the wildfire seasons from July to September.

Figure 2

Flowchart for the inclusion and exclusion of infants in the population-based cohort covering all the infants prenatally exposed to wildfire seasons from 2016 to 2019. *Epiweek means epidemiologic week of the year, where the first epidemiologic week of the year starts on the first Sunday in January.

Figure 3

Time trends of exposure and outcomes of interests by epidemiologic week (epiweek) for infants prenatally exposed during the severe 2017 and 2018 wildfire seasons (red) and the below-average 2016 and 2019 seasons (blue).

Figure 4

Adjusted odds ratios for prenatal exposure to PM_2.5 and all diagnoses of otitis media in the first year of life (red), as well as otitis media diagnoses with associated amoxicillin dispensations (blue). Plot shows the effects of exposures during critical windows of Eustachian tube development (left) and trimesters (right).

Figure 5

Adjusted odds ratios for prenatal exposure to PM_2.5 and all diagnoses of lower respiratory infection in the first year of life (red), as well as lower respiratory infection diagnoses with associated amoxicillin dispensations (blue). Plot shows the effects of exposures during critical windows of lower respiratory tract development (left) and trimesters (right).