Tuberculosis Diagnoses Following Wildfire Smoke Exposure in California

Rationale: Wildfires are a significant cause of exposure to ambient air pollution in the United States and other settings. Although indoor air pollution is a known contributor to tuberculosis reactivation and progression, it is unclear whether ambient pollution exposures, including wildfire smoke, similarly increase risk.

Objectives: To determine whether tuberculosis diagnosis was associated with recent exposure to acute outdoor air pollution events, including those caused by wildfire smoke.

Methods: We conducted a case-crossover analysis of 6,238 patients aged ⩾15 years diagnosed with active tuberculosis disease between 2014 and 2019 in 8 California counties. Using geocoded address data, we characterized individuals’ daily exposure to <2.5 μm-diameter particulate matter (PM2.5) during counterfactual risk periods 3–6 months before tuberculosis diagnosis (hazard period) and the same time 1 year previously (control period). We compared the frequency of residential PM2.5 exposures exceeding 35 μg/m3 (PM2.5 events) overall and for wildfire-associated and nonwildfire events during individuals’ hazard and control periods.

Measurements and Main Results: In total, 3,139 patients experienced 1 or more PM2.5 events during the hazard period, including 671 experiencing 1 or more wildfire-associated events. Adjusted odds of tuberculosis diagnosis increased by 5% (95% confidence interval, 3–6%) with each PM2.5 event experienced over the 6-month observation period. Each wildfire-associated PM2.5 event was associated with 23% (19–28%) higher odds of tuberculosis diagnosis in this time window, whereas no association was apparent for nonwildfire-associated events.

Conclusions: Residential exposure to wildfire-associated ambient air pollution is associated with an increased risk of active tuberculosis diagnosis.