Characterising Carbon Monoxide Household Exposure and Health Impacts in High- and Middle-Income Countries-A Rapid Literature Review, 2010-2024.

Carbon monoxide (CO) is a toxic gas, and faulty gas appliances or solid fuel burning with incomplete combustion are possible CO sources in households. Evaluating household CO exposure models and measurement studies is key to understanding where CO exposures may result in adverse health outcomes. This assists the assessment of the burden of disease in high- and middle-income countries and informs public health interventions in higher-risk environments. We conducted a literature review to identify themes that characterise CO exposure in household dwellings. A keyword-structured search using literature databases was conducted to find studies published in the period of 1 January 2010-5 June 2024. We focused on studies from high- and middle-income countries, excluding animal and biomass studies, and narratively synthesised themes. We identified 5294 papers in the literature search and included 22 papers from thirteen countries in the review. Most measured CO levels were below the WHO or country guidance levels, with sporadic peaks of measured CO linked to fuel-burning activities. To understand CO exposure in households, we identified sixteen themes grouped into five main categories: dwelling characteristics, source characteristics, temporal variation, environmental characteristics, and socioeconomic status of occupants. Seasonal variation (temporal variation), size of room and ventilation (dwelling characteristics), and cooking and outdoor CO levels (source characteristics) had the most evidence. These themes characterising CO exposure in household dwellings are important to aid the development of indoor exposure models and for understanding where CO exposures result in adverse health outcomes. These themes should be validated by household CO monitoring studies, which will enable the identification of higher-risk household dwellings and inform public health actions.