Exposure to Household Air Pollution From Biomass Cooking and Severe Pneumonia in Infants

Importance: Household air pollution from biomass cooking is considered an important risk factor for child pneumonia. Objective: To evaluate the longitudinal association between exposure to particulate matter with a diameter of less than or equal to 2.5 µm (PM_2.5) or carbon monoxide (CO) and severe pneumonia in infants. Design, Setting, and Participants: This cohort study included infants (aged ≤12 months) whose mothers participated in a 4-country randomized clinical trial. Conducted from May 2018 to September 2021, the trial tested whether an 18-month liquefied petroleum gas stove and fuel distribution intervention reduced the incidence of severe pneumonia in offspring during infancy when compared with biomass cooking. The trial was conducted in communities where residents cooked primarily with biomass fuels in Guatemala, India, Peru, and Rwanda. Data analysis was conducted from December 2024 to July 2025. Exposures: Twenty-four hour personal exposure to PM_2.5 and CO was measured 3 times during pregnancy and 3 times during infancy. Main Outcome and Measures: In this exposure-response analysis, severe pneumonia cases were identified using respiratory signs and symptoms with confirmation of consolidation by imaging and hypoxemia by pulse oximetry. The longitudinal association between severe pneumonia in infants and PM_2.5 or CO exposures by infant-quarters, adjusted for confounders, was modeled. Results: Overall, 3061 infants (48.2% girls; mean [SD] gestational age at birth, 39.3 [1.7] weeks) contributed 11996 infant-quarters and 13910 measurements of personal PM_2.5 exposures (range, 5.4-1182.0 µg/m³). A total of 175 episodes of severe pneumonia were identified in 160 infants. Those with at least 1 episode of severe pneumonia had similar mean (SD) prenatal (101 [100] µg/m³ vs 88 [80] µg/m³; P =.11) and postnatal (70 [78] µg/m³ vs 67 [93] µg/m³; P =.68) PM_2.5 exposures when compared with infants without severe pneumonia. There were no associations between prenatal (adjusted risk ratio [RR], 1.03; 95% CI, 0.94-1.13) or postnatal (adjusted RR, 0.97; 95% CI, 0.87-1.09) PM_2.5 exposures and severe pneumonia or between CO exposures and severe pneumonia. Conclusions and Relevance: In this cohort study with exposure-response analysis, there was no evidence of an association between longitudinal PM_2.5 or CO exposures and severe pneumonia in infants. Taken with the intention-to-treat analysis from the randomized clinical trial, these results challenge prior research suggesting that PM_2.5 or CO exposures from biomass cooking are an important risk factor for severe pneumonia in infants.