Oil and gas well development and coccidioidomycosis risk in California: A case-crossover study
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Background
Coccidioidomycosis is an emerging fungal disease caused by inhaling Coccidioides spp. spores. As spores reside in the soil, activities that disturb soil may aerosolize and transport the pathogen, yet the types of activities facilitating transmission remain poorly understood.
Methods
We conducted a case-crossover study to estimate the association between exposure to new oil and gas wells (ie, those in preproduction) and risk of coccidioidomycosis among nearby residents. We obtained information on coccidioidomycosis cases reported between 2007 and 2022 in Kern County, California—a county among the top in both oil and gas production and coccidioidomycosis incidence. We compared exposure to preproduction wells within 5 km of each patient residence during “hazard” and “control” periods using conditional logistic regression.
Findings
During the study period, 73% of Kern County residents lived within 5 km of at least one preproduction well, and 13% lived within 5 km of ≥23 preproduction wells within a single 90-day period. We estimated that the odds of coccidioidomycosis were 11.0% higher (95% CI: 4.3-18.1%) in the 90 days following exposure to at least one preproduction well within 5 km of the patient residence and that the odds of infection increased by 0.7% (95% CI: 0.4-1.0%) for each additional preproduction well within this distance.
Interpretation
We identified a previously unrecognized association between oil and gas development and the transmission of an emerging infectious disease. Given the prevalence of oil and gas development in the study region, its impact on coccidioidomycosis incidence there may be large.
Research in Context
Evidence before the study
Coccidioidomycosis is an emerging fungal disease caused by the inhalation of airborne Coccidioides spores. As these spores reside in the soil, activities that disturb soil—such as construction, farming, earthquakes, and dust storms—have previously been associated with elevated transmission risk. However, the full range of activities that facilitate pathogen transmission remains poorly characterized. Here, we investigated whether oil and gas development contributes to coccidioidomycosis risk as this process involves several soil-disturbing steps (eg, site clearing, leveling, movement of heavy equipment), and occurs at high intensity in an endemic region for the disease. To assess existing evidence, we searched PubMed from database inception to May 27, 2025, for articles published in English using search terms “oil well” OR “gas well” OR “oil and gas construction” OR “oil and gas development” AND “infectious disease” OR “transmission” OR “risk”, and their common textual variants. We identified 31 relevant studies investigating associations between oil and gas development and adverse health outcomes, including preterm birth, low birth weight, cancer diagnoses, upper respiratory symptoms, and all-cause mortality. Only one prior study investigated infectious disease outcomes, finding that high levels of exposure to oil and gas production were associated with moderately elevated COVID-19 severity. We found no prior studies investigating the impact of oil and gas development on the risk of coccidioidomycosis or any other environmental pathogens.
Added value of the study
This study identifies a previously unrecognized adverse health outcome of oil and gas development. Using a case-crossover study design focused on Kern County, California—one of the top seven oil-producing counties in the U.S.—we found the development of new oil and gas wells was associated with elevated coccidioidomycosis risk for individuals within five kilometers. Associations were strongest when the well was developed during fall or summer months, when dry soils may be most readily aerosolized. Further, we found that approximately 73% of Kern County residents lived near at least one well developed over the study period (2007-2022), and 13% lived near ≥ 23 wells developed within a single 90-day period. Given this high level of exposure, oil and gas development may be an important driver of transmission in this highly endemic region.
Implications of all the available evidence
Our study adds to a growing body of evidence of harmful health impacts of oil and gas development. It also identifies a novel pathway of exposure risk for an emerging fungal disease. As there are currently no vaccines available for coccidioidomycosis and few effective antifungal drugs, identifying and mitigating environmental exposures to fungal spores is critical for protecting public health.
