Spirometric Profile of Rural Women Chronically Exposed to Household Biomass Fuel Smoke: A Matched Case-Control Study from Western Kenya

Abstract

Background: Household air pollution arising from the combustion of solid biomass fuel remains a dominant environmental exposure for rural women in sub-Saharan Africa, yet objective lung function data from Kenyan community settings remain scarce. The present study was designed to compare spirometric indices between chronically biomass-exposed rural women and women using clean cooking fuel, and to examine the exposure-response relationship between cumulative smoke exposure and ventilatory impairment. Methods: A matched case-control study was conducted over eighteen months in a rural sub-county of western Kenya. One hundred and fifty never-smoking women aged 20 to 65 years who had cooked exclusively with wood, crop residue or animal dung for at least five years were enrolled as cases, and 150 age-matched women using liquefied petroleum gas were enrolled as controls. A cumulative biomass exposure index, expressed in hour-years, was computed for every participant. Post-bronchodilator spirometry was performed in accordance with the 2019 American Thoracic Society and European Respiratory Society technical standards and interpreted using the Global Lung Function Initiative 2012 reference equations. Comparisons employed the independent samples t test and the chi-square test, and determinants of airflow obstruction were examined by multivariable logistic regression. Results: Cases recorded a substantially higher cumulative exposure index than controls (118.6 plus or minus 52.4 versus 59.7 plus or minus 28.3 hour-years, p less than 0.001). Mean forced expiratory volume in one second as a percentage of predicted was lower among cases (79.3 plus or minus 13.6 versus 90.8 plus or minus 12.1, p less than 0.001), as was the FEV1/FVC ratio (75.4 plus or minus 9.2 versus 80.9 plus or minus 6.4 per cent, p less than 0.001). Airflow obstruction was documented in 26.7 per cent of cases and 10.0 per cent of controls (odds ratio 3.27, 95 per cent confidence interval 1.72 to 6.24, p less than 0.001). The exposure index correlated inversely with FEV1 per cent predicted (r equals minus 0.412, p less than 0.001). Biomass exposure independently predicted obstruction (adjusted odds ratio 2.98, 95 per cent confidence interval 1.48 to 6.00, p equals 0.002). Conclusion: Chronic household biomass smoke exposure was associated with significant and dose-related ventilatory impairment among never-smoking rural Kenyan women, supporting the prioritisation of clean cooking transitions and community spirometry screening.