Roles of Ambient Temperature and PM_2.5 on Childhood Acute Bronchitis and Bronchiolitis from Viral Infection

Studies have associated the human respiratory syncytial virus which causes seasonal childhood acute bronchitis and bronchiolitis (CABs) with climate change and air pollution. We investigated this association using the insurance claims data of 3,965,560 children aged ≤ 12 years from Taiwan from 2006–2016. The monthly average incident CABs increased with increasing PM_2.5 levels and exhibited an inverse association with temperature. The incidence was 1.6-fold greater in January than in July (13.7/100 versus 8.81/100), declined during winter breaks (February) and summer breaks (June–August). The highest incidence was 698 cases/day at <20 °C with PM_2.5 > 37.0 μg/m³, with an adjusted relative risk (aRR) of 1.01 (95% confidence interval [CI] = 0.97–1.04) compared to 568 cases/day at <20 °C with PM_2.5 < 15.0 μg/m³ (reference). The incidence at ≥30 °C decreased to 536 cases/day (aRR = 0.95, 95% CI = 0.85–1.06) with PM_2.5 > 37.0 μg/m³ and decreased further to 392 cases/day (aRR = 0.61, 95% CI = 0.58–0.65) when PM_2.5 was <15.0 μg/m³. In conclusion, CABs infections in children were associated with lowered ambient temperatures and elevated PM_2.5 concentrations, and the high PM_2.5 levels coincided with low temperature levels. The role of temperature should be considered in the studies of association between PM_2.5 and CABs.