Seasonal extreme temperatures and short-term fine particulate matter increases child respiratory hospitalizations in a sparsely populated region of the intermountain western United States

Abstract

Background: Western Montana, USA, experiences complex air pollution patterns with predominant exposure sources from summer wildfire smoke and winter wood smoke. In addition, climate change related temperatures events are becoming more extreme and expected to contribute to increases in hospital admissions for a range of health outcomes. Few studies have evaluated these exposures (air pollution and temperature) that often occur simultaneously and may act synergistically on health.

Methods: We explored short-term exposure to air pollution on childhood respiratory health outcomes and how extreme temperature or seasonal period modify the risk of air pollution-associated hospitalizations. The main outcome measure included all respiratory-related hospital admissions for three categories: asthma, lower respiratory tract infections (LRTI), and upper respiratory tract infections (URTI) across western Montana for all individuals aged 0-17 from 2017-2020. We used a time-stratified, case-crossover analysis and distributed lag models to identify sensitive exposure windows of fine particulate matter (PM_2.5) lagged from 0 (same-day) to 15 prior-days modified by temperature or season.

Results: Short-term exposure increases of 1 μg/m³ in PM_2.5 were associated with elevated odds of all three respiratory hospital admission categories. PM_2.5 was associated with the largest increased odds of hospitalizations for asthma at lag 7-13 days [1.87(1.17-2.97)], for LRTI at lag 6-12 days [2.18(1.20-3.97)], and for URTI at a cumulative lag of 13 days [1.29(1.07-1.57)]. The impact of PM_2.5 varied by temperature and season for each respiratory outcome scenario. For asthma, PM_2.5 was associated most strongly during colder temperatures [3.11(1.40-6.89)] and the winter season [3.26(1.07-9.95)]. Also in colder temperatures, PM_2.5 was associated with increased odds of LRTI hospitalization [2.61(1.15-5.94)], but no seasonal effect was observed. Finally, 13 days of cumulative PM_2.5 prior to admissions date was associated with the greatest increased odds of URTI hospitalization during summer days [3.35(1.85-6.04)] and hotter temperatures [1.71(1.31-2.22)].

Conclusions: Children's respiratory-related hospital admissions were associated with short-term exposure to PM_2.5. PM_2.5 associations with asthma and LRTI hospitalizations were strongest during cold periods, whereas associations with URTI were largest during hot periods.

Classification: environmental public health, fine particulate matter air pollution, respiratory infections.

Keywords: Montana; PM2.5; asthma; case-crossover design; environmental health; hospital discharge data; lag effects; lower respiratory tract infections; rural; upper respiratory tract infections; wildfire.

Figure 1. Study Area Population.

45 ZCTAs in western Montana included in study area symbolized by percent total population. Hospital location (ZCTA = 59804) represented by red circle.

Figure 2. Respiratory Hospital Admissions and PM_2.5.

Related hospital visits for asthma (dotted line), lower respiratory tract infections (LRTI–dashed line), and upper respiratory tract infections (URTI–solid line), by week, for western Montana residents, aged 0–17. Average PM_2.5, shown in dot-dashed line for the entire study area, for comparison.

Figure 3. Children’s Upper Respiratory Tract Infection Risk for Hospital Admissions with Short-Term Exposure to PM2.5.

Case cross-over results for distributed lag models of PM2.5 for delays in cumulative days for (A) the Main PM2.5 model–only PM2.5, (B) the Temperature model–PM2.5xTemperature displayed for three levels of hotter (red), median (green) and colder (blue) temperatures, and (C) the Season model–PM_2.5xSeason displayed for the four levels of Fall (maroon), Winter (blue), Spring (light green), and Summer (green).