Chronic low exposure to air pollution in early life linked to allergic lung diseases in children

According to the researchers, this is the first study to investigate allergic sensitisation concerning exposure to air pollution from a landscape fire in a non-occupational setting. They did not observe a relationship between in-utero exposure or exposure during the first 2 years following the birth to PM2.5 (particulate matter with an aerodynamic diameter < 2.5 μm) emitted by coal smoke and allergic sensitisation, but increased background PM2.5 concentrations were tied to a higher prevalence of sensitisation to dust.

In terms of sensitisation to specific allergens, amongst the tested allergens, the only positive association was found with dust.

There is inconsistent evidence on the relationship between air pollution and allergic sensitisation in childhood, and this relationship has not been investigated in the context of smoke events predicted to increase with climate change. Thus, Myriam Ziou, University of Tasmania, Hobart, Tasmania, Australia, and colleagues aimed to evaluate associations between exposure in two early life periods to severe levels of PM2.5 from a mine fire, background PM2.5, and allergic sensitisation later in childhood.

For this purpose, they measured specific immunoglobulin E (IgE) levels for seven aeroallergens and total IgE levels in a cohort of children exposed to the Hazelwood coal mine fire, either in utero or during the first two years, in a region in Australia where ambient levels of PM2.5 are generally low.

They estimated personal exposure to fire-specific PM2.5 emissions based on a high-resolution meteorological and pollutant dispersion model and detailed reported movements of pregnant mothers and young children during the fire. The usual exposure to PM2.5 at the residential address at birth was also estimated using a national satellite-based land-use regression model.

Associations between PM2.5 sources and sensitization to cat, dust, grass, and fungi were estimated seven years after the fire with logistic regression, while associations with total IgE levels were estimated with linear regression.

One hundred three children presenting to the 2021 clinical follow-up agreed to provide a blood sample. Those born overseas (n=2) were excluded as their background exposure could not be estimated accurately, which led to the inclusion of 101 children. Of 101 children, 50 were born before the start of the fire, four were born during the fire, 29 were in utero during the whole fire period, and 18 were conceived after the fire.

The study led to the following findings:

• Sensitisation to D. pteronyssinus had the highest prevalence (35.4%), while Cl. herbarum had the lowest (2.0%).
• There were various levels of correlation between sensitisation to allergens from different categories, the strongest being between perennial rye grass pollen and D. pteronyssinus.
• No association was found between the levels of fire-related PM2.5 and the odds of sensitisation to any of the distinct allergen categories, for both peak and cumulative exposure. Exposure to fire-related PM2.5 was not linked with sensitisation to any category either.
• Early life background exposure to PM2.5 was positively associated with the odds of being sensitised to dust (adjusted OR = 1.90), but not with cat, grass, fungi, or overall sensitization.
• No evidence was observed of a relationship between exposure to fire-related or background PM2.5 and overall total IgE in the blood.

"Our study indicates chronic exposure to relatively low air pollution levels in early life could have a stronger association with atopy development than time-limited high levels, which may be part of the mechanism relating air pollution to allergic diseases, such as atopic dermatitis and allergic rhinitis," the researchers wrote.

"Larger studies are needed to examine periods of increased risk during pregnancy and infancy based on knowledge of the maturation of the immune system," they concluded.

Reference:

Ziou, M., Gao, C.X., Wheeler, A.J. et al. Exposure to air pollution concentrations of various intensities in early life and allergic sensitisation later in childhood. BMC Pulm Med 23, 516 (2023). https://doi.org/10.1186/s12890-023-02815-8