Wildfire smoke exposure and emergency department visits for headache: A case‐crossover analysis in California, 2006–2020

Abstract

Objective To evaluate the association of short‐term exposure to overall fine particulate matter of <2.5 μm (PM2.5) and wildfire‐specific PM2.5 with emergency department (ED) visits for headache. Background Studies have reported associations between PM2.5 exposure and headache risk. As climate change drives longer and more intense wildfire seasons, wildfire PM2.5 may contribute to more frequent headaches. Methods Our study included adult Californian members (aged ≥18 years) of a large de‐identified commercial and Medicare Advantage claims database from 2006 to 2020. We identified ED visits for primary headache disorders (subtypes: tension‐type headache, migraine headache, cluster headache, and “other” primary headache). Claims included member age, sex, and residential zip code. We linked daily overall and wildfire‐specific PM2.5 to residential zip code and conducted a time‐stratified case‐crossover analysis considering 7‐day average PM2.5 concentrations, first for primary headache disorders combined, and then by headache subtype. Results Among 9898 unique individuals we identified 13,623 ED encounters for primary headache disorders. Migraine was the most frequently diagnosed headache (N = 5534/13,623 [47.6%]) followed by “other” primary headache (N = 6489/13,623 [40.6%]). For all primary headache ED diagnoses, we observed an association of 7‐day average wildfire PM2.5 (odds ratio [OR] 1.17, 95% confidence interval [CI] 0.95–1.44 per 10 μg/m3 increase) and by subtype we observed increased odds of ED visits associated with 7‐day average wildfire PM2.5 for tension‐type headache (OR 1.42, 95% CI 0.91–2.22), “other” primary headache (OR 1.40, 95% CI 0.96–2.05), and cluster headache (OR 1.29, 95% CI 0.71–2.35), although these findings were not statistically significant under traditional null hypothesis testing. Overall PM2.5 was associated with tension‐type headache (OR 1.29, 95% CI 1.03–1.62), but not migraine, cluster, or “other” primary headaches. Conclusions Although imprecise, these results suggest short‐term wildfire PM2.5 exposure may be associated with ED visits for headache. Patients, healthcare providers, and systems may need to respond to increased headache‐related healthcare needs in the wake of wildfires and on poor air quality days.

Effect of wildfire smoke on primary headache disorders remains unclear

“…In the study “Wildfire Smoke Exposure and Emergency Department Visits for Headache: A Case‐Crossover Analysis in California, 2006–2020,” the authors attempt to determine effect of wildfire smoke particulate matter on headache outcomes while controlling for confounding variables such as time of year 2 . A private insurance claims database was used to identify Emergency Department (ED) visits in adult patients with headache (or a headache subtype) as one of the first three visit diagnoses, with >13,000 ED visits in California by 9,898 unique individuals included.…”

Migraine and air pollution: A systematic review

“…Point estimates for the association between migraine and relatively higher PM 10 or PM 2.5 ranged from 0.97 to 3.09 20,22,44,46–49 . For PM 10 and PM 2.5 , 3/3 (100%) and 10/11 (91%) of estimates, respectively, were above the null.…”

“…Given that holidays are relatively rare, this would not be expected to strongly influence results. One short‐term study met the criteria for high risk of confounding bias due to missing the critical confounder temperature, 44 while a long‐term study from 1994 did not report on the critical confounder body mass index 45 . Finally, one study scored low risk of bias by including all of the confounders listed as critical or potential 46 …”

Health effects of wildfires

“…Recent literature has documented worsened cognitive outcomes, 88,89 declines in mental health, 24 and increased ED visits for headaches 90 associated with exposure to wildfire smoke. For example, Cleland et al 88 assessed cognitive performance among adults and found that wildfire smoke plumes was negatively associated with the estimated attention score on the same day and one week later.…”