Co-exposure to planned power outages and wildfire PM2.5 and acute healthcare utilization in California: A time-stratified case-crossover study

BACKGROUND: To prevent wildfires, electric utilities may preemptively de-energize power lines (public safety power shutoffs [PSPS]). These PSPS events may unintentionally harm health, particularly for those with pre-existing conditions like chronic obstructive pulmonary disease (COPD) or who rely on electricity-dependent medical equipment. Health impacts may worsen further if a wildfire occurs despite the power shutoff. To assess the effect of PSPS events, wildfire fine particulate matter (PM2.5) exposure, and their co-occurrence on cause-specific healthcare utilization. METHODS AND FINDINGS: We identified PSPS events in California from 2013 to 2019, categorizing magnitude based on number of people without power by zip code. We leveraged zip code-level average daily wildfire PM2.5 estimates and respiratory, COPD-specific, cardiovascular, and psychiatric emergency department visits and unscheduled hospital admissions among adults aged 20+ from the California Department of Health Care Access and Information. Using a time-stratified case-crossover design, we estimated the impact of same-day and lagged PSPS events alone, wildfire PM2.5 alone, and their co-occurrence on healthcare utilization, adjusting for daily temperature. Severe PSPS events were associated with elevated odds of same-day respiratory encounters (OR = 1.06, 95% CI: 1.02, 1.11) and lag0-3 effects were similar. These associations were stronger for COPD. Compared to no PSPS or wildfire exposure, joint PSPS and 10 μg/m3 higher wildfire PM2.5 was associated with higher odds of respiratory encounters (1.16 [95% CI: 1.10, 1.22]), with evidence of multiplicative interaction. Associations were null for cardiovascular and psychiatric encounters. Limitations include exposure misclassification, because we assigned exposure at the residential zip code level, aggregating circuit-level data and not accounting for individual behavior or the potential for PSPS events to impact wildfire PM2.5 exposure. CONCLUSIONS: PSPS events may increase risk of respiratory events requiring acute care utilization, especially when they co-occur with wildfire PM2.5.