Coccidioidomycosis and COVID-19 Co-Infection, United States, 2020

Alexandra K. Heaney; Jennifer R. Head; Kelly Broen; Karen Click; John Taylor; John R. Balmes; Jon Zelner; Justin V. Remais


Emerging Infectious Diseases. 2021;27(5):1266-1273. 

In This Article

Areas for Future Research

Cloth Masks

Although cloth masks are a critical control method for COVID-19 (Appendix), studies have not examined the efficacy of cloth masks for filtering Coccidioides arthroconidia. At 2–5 μm in diameter, Coccidioides arthroconidia are substantially larger than SARS-CoV-2; this size difference might lead to differing levels of filtration effectiveness (Appendix references 99,100). One study found that cloth masks containing tightly woven cottons can filter 98% of particles in the 300 nm–6 μm range (Appendix reference 101), yet such results are difficult to extrapolate to specific particles such as Coccidioides arthroconidia (Appendix reference 102). It is also difficult to extrapolate results to other cloth masks, which vary widely in their filtration properties. Furthermore, leakage from improperly fitting masks can reduce efficacy of particle filtration by up to 50% (Appendix reference 101). The effects of leakage on disease prevention might differ on the basis of infectious dose; although a single Coccidioides spore might confer infection, the infectious dose of SARS-CoV-2 is probably higher. California therefore requires employers with worksites in regions to which coccidioidomycosis is endemic to provide respiratory protection filters rated at least N95 to workers if dust cannot be controlled; no mask recommendation exists for the general public (Appendix reference 103).


Transmission of SARS-CoV-2 and Coccidioides spores might be influenced by climatic conditions, such as temperature and humidity, that can affect pathogen survival and transport. For example, high humidity can suppress aerosol transmission of respiratory pathogens such as influenza and respiratory syncytial virus (Appendix references 104–110). Early research in Wuhan, China, suggested that SARS-CoV-2 might be transmitted more efficiently in less humid environments (Appendix references 111–113; W. Luo, unpub. data, Although the influence of temperature and other climatic conditions on transmission and seasonality of SARS-CoV-2 currently might be outweighed by the large size of the susceptible population, the introduction of a vaccine could result in patterns of population immunity that enable climate to play a larger moderating role (Appendix reference 114). Because relative humidity plays a major role in regulating atmospheric dust concentrations, high atmospheric moisture can limit the dispersal of Coccidioides spores, potentially suppressing coccidioidomycosis transmission. For example, under wind conditions strong enough to mobilize dust, increases in relative humidity were associated with decreasing atmospheric dust concentrations (Appendix reference 115).

Disparities in Surveillance

The extent of socioeconomic, demographic, racial, and other disparities in COVID-19 and coccidioidomycosis is probably greater than reflected in administrative data sources. For example, analyses from hard-hit regions have indicated that high rates of excess death probably reflect a large burden of unreported SARS-CoV-2 infection (Appendix reference 116; J. Felix-Cardoso, unpub. data, Although testing coverage for SARS-CoV-2 is increasing, infections will probably continue to be undercounted in certain regions and populations because of factors such as disparate healthcare access, reagent shortages, and varied willingness to get tested. Undocumented or migrant farmworkers at high risk for exposure to Coccidioides spores are mostly uninsured, ineligible for healthcare benefits, or unable to afford healthcare (Appendix reference 117,118). The disparities seen in rates of illness and death caused by COVID-19 and coccidioidomycosis might have many contributing factors, including barriers to affordable, high-quality, and accessible healthcare; occupational exposures; mass incarceration; residential segregation; discrimination; and differential rates of concurrent conditions. Understanding these disparities is critical for attracting the attention and resources needed to remedy inequities in exposures, care-seeking, and illness and death caused by coccidioidomycosis and COVID-19.