Respiratory and atopic conditions in children two to four years after the 2014 Hazelwood coalmine fire

This is a very strange study.  It is about health effects of exposure to smoke pollution from one fire. But they had no baseline for a before and after study.  So they sought to get around that by correlating ESTIMATED monthly exposure to pollution with monthly reports of ill health.

But one would assume that almost all the pollution from the fire would have occurred WITHIN the first month.  How could there be ANY effect up to four years later?  It's a mystery. I have read and re-read the article several times but can make no sense of it

Abstract

Objective: To evaluate associations between exposure during early life to mine fire smoke and parent‐reported indicators of respiratory and atopic illness 2–4 years later.

Design, setting: The Hazelwood coalmine fire exposed a regional Australian community to markedly increased air pollution during February – March 2014. During June 2016 – October 2018 we conducted a prospective cohort study of children from the Latrobe Valley.

Participants: Seventy‐nine children exposed to smoke in utero, 81 exposed during early childhood (0–2 years of age), and 129 children conceived after the fire (ie, unexposed).

Exposure: Individualised mean daily and peak 24‐hour fire‐attributable fine particulate matter (PM2.5) exposure during the fire period, based on modelled air quality and time‐activity data.

Main outcome measures: Parent‐reported symptoms, medications use, and contacts with medical professionals, collected in monthly online diaries for 29 months, 2–4 years after the fire.

Results: In the in utero exposure analysis (2678 monthly diaries for 160 children exposed in utero or unexposed), each 10 μg/m3 increase in mean daily PM2.5 exposure was associated with increased reports of runny nose/cough (relative risk [RR], 1.09; 95% CI, 1.02–1.17), wheeze (RR, 1.56; 95% CI, 1.18–2.07), seeking health professional advice (RR, 1.17; 95% CI 1.06–1.29), and doctor diagnoses of upper respiratory tract infections, cold or flu (RR, 1.35; 95% CI, 1.14–1.60). Associations with peak 24‐hour PM2.5 exposure were similar. In the early childhood exposure analysis (3290 diaries for 210 children exposed during early childhood, or unexposed), each 100 μg/m3 increase in peak 24‐hour PM2.5 exposure was associated with increased use of asthma inhalers (RR, 1.26; 95% CI, 1.01–1.58).

Conclusions: Exposure to mine fire smoke in utero was associated with increased reports by parents of respiratory infections and wheeze in their children 2–4 years later.

Med J Aust doi: 10.5694/mja2.50719
Published online: 24 August 2020