Respiratory health effects of occupational biomass smoke exposure among cook cum helpers in rural Assam school kitchens using propensity score matching

The use of biomass fuel in households has many adverse health effects and the use of such fuel in cooking environments as an occupational exposure setting remain unexplored. This study aims to examine the extent of respiratory health risks, as a consequence of exposure to biomass fuel smoke, of cook-cum-helpers of the Mid-Day Meal scheme in rural Assam, India. We utilized a comparative cross sectional study design to investigate 130 cook-cum-helpers from 28 government schools (65 from firewood kitchens and 65 from LPG kitchens). The respiratory symptoms of participants were documented using the standard American Thoracic Society (ATS) questionnaire and pulmonary function tests were conducted using spirometry. Based on the confounders of household biomass exposure and passive smoking, propensity score matching was employed. The Average Treatment Effect on the Treated (ATET) approach was used and matched regression models were computed in the presence of cluster standard school level errors. The mixed effects and cluster adjusted models were used to conduct sensitivity analyses. Of the matched study population ( n = 116) firewood exposure was found to increase the probability of reporting at least one respiratory symptom by 28.4% points (95% CI 15.6–41.2) and airway obstruction by 22.1% points (95% CI 8.4–35.8). Those firewood exposed workers experienced a 13.95% point greater decline in the mean FEV₁ percent-predicted. A significant exposure–duration gradient (p-trend < 0.001) was found that supports the increase in respiratory health risks with longer durations of employment. These findings were valid across different specifications. Institutional school kitchens that utilize biomass fuel are an occupational health hazard that has and continues to remain underestimated. These findings underscore the need to improve occupational health policies and accelerate the use of clean cooking fuels. However, the cross-sectional design of the study limits causal analysis.