Abstract
IMPORTANCE: January 2025 brought devastating wildfires to Los Angeles (LA) County, California, causing poor air quality, destroying homes and businesses, and displacing thousands of people. OBJECTIVE: To promptly determine if the January 2025 LA fires increased outpatient acute health care utilization. DESIGN, SETTING, AND PARTICIPANTS: This cohort study assessed electronic health care records of 3.7 million members of Kaiser Permanente Southern California (KPSC) who met enrollment criteria. Of those, 305 258 were highly exposed and 1.4 million were moderately exposed. KPSC serves 4.7 million people across 10 counties. Analyses were conducted January-June 2025. EXPOSURES: Highly exposed members were those who resided in a census tract within 20 km of burn zones, and moderately exposed members were those who resided in tracts that were 20 km or more miles from the burn zones but within LA County. The maximum wildfire burn zone reached by an LA or Ventura county wildfire by January 17, 2025 was used. MAIN OUTCOMES AND MEASURES: Daily outpatient and virtual acute care visits in 5 categories: all-cause (or any medical reason), cardiovascular, injury, neuropsychiatric, and respiratory were identified and analyzed by a 2-stage interrupted time-series model using machine-learning algorithms to determine if and by how much the January 2025 LA fires increased outpatient acute health care utilization. RESULTS: Across the week following the January 7 LA fires' ignition, there were excess visits from the 3.7 million study population (1.94 million women [52.2%], 1.77 million men [47.7%]; median age, 42 years [IQR, 21-62]; 11.5% Asian, 7.8% Black, 43.8% Hispanic, and 29% White). Virtual respiratory visits were 42% (95% empirical CI, 23%-60%) higher than expected in highly exposed groups and 36% (95% empirical CI, 19%-54%) higher than expected in moderately exposed groups. Similarly, the highly exposed and moderately exposed groups had 44% and 40% more than expected virtual cardiovascular visits, respectively, and 27% and 31% more than expected outpatient respiratory visits, respectively (n=2866 and n=5166 total excess visits). All-cause virtual care visits were also elevated in the moderately exposed group, potentially representing displaced in-person care. Among highly exposed members, outpatient and virtual injury visits and outpatient neuropsychiatric visits were 18% higher than expected on January 7. Extrapolating to all insured LA County residents, an excess of 15 792 cardiovascular and 18 489 respiratory virtual care visits and 27 903 respiratory outpatient visits was estimated during the week following ignition. CONCLUSIONS AND RELEVANCE: This cohort study observed substantial increases in acute health care utilization, especially virtual care-seeking following the LA fires. As disruptive climate events increase, such data are essential to inform health care preparedness and response.