Coccidioides skin test performance and patterns of prior immunity to coccidioidomycosis among a large population of males entering California state prisons, 2015-2024: a population-based modelling study

Jennifer R Head; Andrew F Brouwer; Arundhati Rajan; Marlena Scherer; Monica Williams; John Balmes; George R Thompson 3rd; Neil M Ampel; Kimberley D Lucas

doi:10.1016/j.lana.2026.101461

Coccidioides skin test performance and patterns of prior immunity to coccidioidomycosis among a large population of males entering California state prisons, 2015-2024: a population-based modelling study

Lancet Reg Health Am. 2026 Mar 26:58:101461. doi: 10.1016/j.lana.2026.101461. eCollection 2026 Jun.

Authors

Jennifer R Head^{1

2}, Andrew F Brouwer¹, Arundhati Rajan³, Marlena Scherer⁴, Monica Williams⁵, John Balmes⁶, George R Thompson 3rd⁷, Neil M Ampel⁸, Kimberley D Lucas⁴

Affiliations

¹ Department of Epidemiology, School of Public Health, University of Michigan, Ann Arbor, MI, USA.
² Institute of Global Change Biology, University of Michigan, Ann Arbor, MI, USA.
³ Department of Biostatistics, School of Public Health, University of Michigan, Ann Arbor, MI, USA.
⁴ California Correctional Health Care Services, Public Health Services, Elk Grove, CA, USA.
⁵ California Correctional Health Care Services, North Kern State Prison, Nursing Services, Delano, CA, USA.
⁶ Division of Environmental Health Sciences, School of Public Health, University of California, Berkeley, Berkeley, CA, USA.
⁷ Department of Internal Medicine, Division of Infectious Diseases and the Department of Medical Microbiology and Immunology, University of California Davis Medical Center, Sacramento, CA, USA.
⁸ College of Medicine, University of Arizona, Tucson, AZ, USA.

Abstract

Background: The incidence of coccidioidomycosis-an emerging fungal infection-is high within California state prisons. In 2015, California began offering a Coccidioides skin test, Spherusol®, to adult males upon entry into prison, with those susceptible to coccidioidomycosis restricted from placement in two prisons with highest incidence. This study aimed to understand test performance within the incarcerated population and to estimate population-level immunity and force of infection (FOI) by age and pre-incarceration residence.

Methods: We fit catalytic models to skin test data from 154,450 males aged 18 to 64 years incarcerated in California state prisons between January 11, 2015, and September 15, 2024.

Findings: Estimated test sensitivity was 48.8% (95% confidence interval (CI): 45.1-52.6%). Low sensitivity was attributed to waning reactivity, estimated at 5.3% (95% credible interval (CrI): 4.3, 6.3%) loss in reactivity per year since infection. We estimated a prevalence of prior infection among males from the hyperendemic Kern County of 17.9% (95% CrI: 12.1, 26.0) at 18 years and 94.7% (95% CrI: 89.8, 97.4) by 65 years, and an annual average FOI in Kern County of 54.8 new infections per 1000 susceptible males (95% CrI: 41.6, 70.0). Regions outside the highly endemic area demonstrated lower, but non-negligible, prevalences of prior infection; prior infection prevalence among San Francisco Bay Area male residents reached 16.9% (95% CrI: 13.3, 21.2) by age 65.

Interpretation: These findings update our understanding of population immunity to coccidioidomycosis among California males entering prison and inform disease risk in this high-risk population.

Funding: NIHNIAID K01AI173529.

Keywords: Coccidioidomycosis; Immunity; Incarcerated; Prior infection; Skin test; Spherulin; Valley fever.