Association between wildfires and coccidioidomycosis incidence in California, 2000-2018: a synthetic control analysis

Sophie Phillips; Isabel Jones; Gail Sondermyer-Cooksey; Alexander T Yu; Alexandra K Heaney; Bo Zhou; Abinash Bhattachan; Amanda K Weaver; Simon K Campo; Whitney Mgbara; Robert Wagner; John Taylor; Dennis Lettenmaier; Gregory S Okin; Seema Jain; Duc Vugia; Justin V Remais; Jennifer R Head

doi:10.1097/EE9.0000000000000254

Association between wildfires and coccidioidomycosis incidence in California, 2000-2018: a synthetic control analysis

Environ Epidemiol. 2023 Jun 12;7(4):e254. doi: 10.1097/EE9.0000000000000254. eCollection 2023 Aug.

Authors

Sophie Phillips¹, Isabel Jones², Gail Sondermyer-Cooksey³, Alexander T Yu³, Alexandra K Heaney², Bo Zhou⁴, Abinash Bhattachan⁵, Amanda K Weaver², Simon K Campo², Whitney Mgbara², Robert Wagner⁶, John Taylor⁶, Dennis Lettenmaier⁴, Gregory S Okin⁴, Seema Jain³, Duc Vugia³, Justin V Remais², Jennifer R Head^{1

2}

Affiliations

¹ Department of Statistics, University of California, Los Angeles, Los Angeles, California.
² Division of Environmental Health Sciences, School of Public Health, University of California, Berkeley, Berkeley, California.
³ Infectious Diseases Branch, California Department of Public Health, Richmond, California.
⁴ Department of Geography, University of California, Los Angeles, Los Angeles, California.
⁵ Department of Geosciences, Texas Tech University, Lubbock, Texas.
⁶ Department of Plant and Microbial Biology, College of Natural Resources, University of California, Berkeley, Berkeley, California.

Abstract

The frequency and severity of wildfires in the Western United States have increased over recent decades, motivating hypotheses that wildfires contribute to the incidence of coccidioidomycosis, an emerging fungal disease in the Western United States with sharp increases in incidence observed since 2000. While coccidioidomycosis outbreaks have occurred among wildland firefighters clearing brush, it remains unknown whether fires are associated with an increased incidence among the general population.

Methods: We identified 19 wildfires occurring within California's highly endemic San Joaquin Valley between 2003 and 2015. Using geolocated surveillance records, we applied a synthetic control approach to estimate the effect of each wildfire on the incidence of coccidioidomycosis among residents that lived within a hexagonal buffer of 20 km radii surrounding the fire.

Results: We did not detect excess cases due to wildfires in the 12 months (pooled estimated percent change in cases: 2.8%; 95% confidence interval [CI] = -29.0, 85.2), 13-24 months (7.9%; 95% CI = -27.3, 113.9), or 25-36 months (17.4%; 95% CI = -25.1, 157.1) following a wildfire. When examined individually, we detected significant increases in incidence following three of the 19 wildfires, all of which had relatively large adjacent populations, high transmission before the fire, and a burn area exceeding 5,000 acres.

Discussion: We find limited evidence that wildfires drive increases in coccidioidomycosis incidence among the general population. Nevertheless, our results raise concerns that large fires in regions with ongoing local transmission of Coccidioides may be associated with increases in incidence, underscoring the need for field studies examining Coccidioides spp. in soils and air pre- and post-wildfires.

Keywords: California; Climate change; Coccidioides; Coccidioidomycosis; Drought; Synthetic control; Valley fever; Wildfires.

Grants and funding

R01 AI148336/AI/NIAID NIH HHS/United States