By Stan Deresinski, MD, FACP, FIDSA

Clinical Professor of Medicine, Stanford University

Dr. Deresinski reports no financial relationships relevant to this field of study.

SYNOPSIS: Another occupational outbreak of coccidioidomycosis in solar farm workers in an endemic area points to the continued risk and the difficulty of preventing such occurrences.

SOURCE: Laws RL, Cooksey GS, Jain S, et al. Coccidioidomycosis outbreak among workers constructing a solar power farm — Monterey County, California, 2016-2017. MMWR Morb Mortal Wkly Rep 2018;67:931-934.

The California Department of Public Health (CDPH) was notified in January 2017 of the occurrence of coccidioidomycosis in three workers involved in the construction of a solar power installation in southeastern Monterey County. The investigators ultimately identified nine cases among the 2,410 solar farm workers. The incidence among the workers was 1,095 per 100,000 persons/year, a rate that was 4.4-210.6 times higher than the background rate in the counties in which the cases resided (Fresno, Madera, Monterey, and San Luis Obispo). The incidence in the workers was 62.6 times higher than that in Monterey County.

Eight of the nine patients were available for interview. Six had received a diagnosis of pneumonia. Five patients had visited emergency departments one to five times, and one patient was hospitalized; none died. Seven of those interviewed had missed work as the result of the illness for a median of 14 days, but with a range of 1-320 days. The job titles of the patients included biologist, paleontologist, electrician, truck driver, iron worker, and general laborer.

The first patients became ill in August and the last in December, when seasonal rains controlled the dust, which the patients reported to be problematic. (See Figure 1.) Although attempts had been made to follow recommendations that emerged from previous outbreaks at California solar farms, the implementation proved inadequate, and CDPH has made further recommendations revolving around dust control, respiratory protection, and improved awareness of the risk and symptoms of coccidioidomycosis.


Outbreaks of coccidioidomycosis are a relatively common occurrence, with 47 involving 1,464 cases published between 1940 and 2015, with more than half caused by occupational exposures.1 In addition to outbreaks involving solar farm workers, other recent occupational outbreaks of coccidioidomycosis in California have included highway workers, prisoners, and U.S. Navy SEALS undergoing training.

There undoubtedly will be more to come. On Sept. 10, 2018, California Gov. Jerry Brown signed legislation requiring that by 2030, 60% of electricity used in the state be generated from renewable sources and that this proportion will increase to 100% by 2045. A significant contribution to this switch to renewables in the fifth largest economy in the world is and will be solar energy.

Solar farms are built in rural areas (large areas of land are needed) and where the sun shines the most. In California, the Central Valley, including the San Joaquin Valley, fits the bill. Unfortunately, the construction of solar farms kicks up a lot of dust and, in such locations, that means the aerosolization of Coccidioides immitis arthroconidia. And there is more to come for other reasons, such as the current construction of California High-Speed Rail down the spine of the Central Valley.


  1. Freedman M, Jackson BR, McCotter O, Benedict K. Coccidioidomycosis outbreaks, United States and worldwide, 1940-2015. Emerg Infect Dis 2018;24:417-423.

Figure 1: Construction Schedule and Illness Onset of Coccidioidomycosis Among Workers Constructing a Solar Power Farm (N = 9) — Monterey County, California, 2016-2017

Figure 1

Source: Centers for Disease Control and Prevention