Wildfire and Landscape Fire Smoke Exposure and the Risk of Acute Respiratory Infection in Children: A Systematic Review and Meta-Analysis

Abstract

Background: Landscape fires are increasing and children are physiologically more vulnerable to smoke than adults. Acute respiratory infection remains a leading cause of death under five years. One previous meta-analysis pooled upper respiratory infection alone; the most recent systematic review pooled no data.

Objective: To quantify the association between exposure to smoke from wildfire and other landscape fires and the risk of acute respiratory infection in children and adolescents aged 0-19 years, and to assess differences by age, exposure window, income setting, and outcome definition.

Methods: Six Boolean strings were run in PubMed and MEDLINE (1,016 unique records). Observational studies reporting an effect estimate with 95% confidence interval for acute respiratory infection at ages 0-19 years exposed to landscape fire smoke were eligible. As no study reported means and standard deviations, pooling used the log-ratio scale with a random-effects DerSimonian-Laird model. Continuous and categorical contrasts were pooled separately. Risk of bias used ROBINS-E and the Newcastle-Ottawa Scale.

Results: Eighteen studies were included and seventeen pooled. In the continuous pool (k = 12), each 10 µg/m³ increment of fire-related particulate matter gave a relative risk of 1.104 (95% CI 1.070-1.139; Hartung-Knapp 1.042-1.171), I² 92%, prediction interval 1.015-1.201. Restricted to infection-specific outcomes (k = 8) it was 1.148 (1.067-1.234). Risk was higher under five years (1.202, 1.104-1.309) than in unstratified 0-19 year populations (1.018, 1.001-1.035; p < 0.001) and after prenatal than postnatal exposure (1.239 versus 1.077; p < 0.001). Egger’s test indicated small-study effects (p = 0.0006); trim-and-fill gave 1.067 (1.036-1.099). A categorical pool (k = 5) gave an unstable 1.940 (1.269-2.967).

Conclusion: Fire-related particulate exposure was associated with a modest but consistent increase in the risk of acute respiratory infection in children, concentrated in those under five years and after prenatal exposure.