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. While 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 over the years 2014-2019 in 8 California counties. Using geocoded address data, we characterized individuals’ daily exposure to <2.5µm-diameter particulate matter (PM2.5) during counterfactual risk periods 3-6 months before tuberculosis diagnosis (hazard period), and the same time one year previously (control period). We compared the frequency of residential PM2.5 exposures exceeding 35µg/m3 (PM2.5 events), overall and for wildfire-associated and non-wildfire events, during individuals’ hazard and control periods. Measurements and Main Results: In total, 3,139 patients experienced ≥1 PM2.5 event during the hazard period, including 671 experiencing ≥1 wildfire-associated event. Adjusted odds of tuberculosis diagnosis increased by 5% (95% confidence interval: 3-6%) with each PM2.5 event experienced over the 6-month observation periods. 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 non–wildfire-associated events. Conclusions: Residential exposure to wildfire-associated ambient air pollution is associated with increased risk of active tuberculosis diagnosis.