Attributable risk of household solid fuel use and second-hand smoke associated with under-5 mortality in 46 low- and lower-middle-income countries, 2010-2020.

Background: Household solid fuel use (including indoor and outdoor) and second-hand smoke (SHS) are considered to be major contributors of under-5 mortality (U5M) in low- and lower-middle-income countries (LMICs). This study provides a comprehensive assessment of their odds ratios and attributable mortality in LMICs.

Methods: We used the Demographic Health Surveys data for under-5 children in 46 LMICs (n = 778,532) from 2010 to 2020. Mixed effect multilevel logistic regressions were conducted to estimate the pooled adjusted odds ratio (aOR) for U5M due to solid fuel use, SHS and their combination compared to no exposure to them in 46 LMICs. The attributable mortality of solid fuel use, SHS, and their combination were assessed for each LMIC.

Findings: The pooled aOR of solid fuel use and SHS for U5M was estimated to be 1.27 (95% Confidence Interval (CI): 1.19-1.36) and 1.13 (95%CI: 1.06-1.25), respectively, whereas those of their combination was 1.40 (95%CI: 1.31-1.50). U5M attributable to indoor and outdoor solid fuel use was the highest in Myanmar (18.0%) and the Gambia (16.5%), respectively, while those attributable to SHS was the highest in Indonesia (9.8%). U5M attributable to the combination of solid fuel use and SHS was the highest in Timor-Leste (22.7%).

Interpretation: The combined effect of exposure to solid fuel and SHS had a higher risk of U5M than the individual risk. The use of clean fuel and tobacco control measures should be integrated with other child health promotion policies.

Funding: This research was partially supported by a research grant from the Ministry of Education, Culture, Sports, Science and Technology of Japan (21H03203).