1180. Seroincidence and Risk of Coccidioidomycosis Infection Among Active Duty Personnel Stationed at Naval Air Station Lemoore in the San Joaquin Valley of California

BACKGROUND: Coccidioidomycosis ranges clinically from a self-limited respiratory illness to multi-organ dissemination. Based largely on skin testing from the 1940s, 60% of infections are thought to be asymptomatic. Limited Coccidioides seroincidence data support our understanding of the epidemiology and pathogenicity of this disease. METHODS: This retrospective cohort study tested 2000 U.S. military personnel for Coccidioides exposure after transfer to an endemic region of California between 2011 and 2017. The presence of IgG and IgM anti-Coccidioides antibodies were tested on pre- and post-transfer serum samples from the DoD Serum Repository to establish rates of seroconversion. Medical histories and participant demographics including race/ethnicity and military occupational specialty codes were collected from the electronic medical record and participants were stratified by a history of Coccidioides-specific or general respiratory illness based on ICD9/ICD10 coding. RESULTS: Thirty of 2000 participants tested newly positive for anti-Coccidioides antibodies after 12 months on station. Seroconversion incidence varied from 0.0-1.32 annually and overall 0.5 per 100 person years. Seroconverters were more frequently diagnosed with coccidioidomycosis or pneumonia than non-converters (p=0.027). No statistically significant association between demographic characteristics and seroconversion or disease was observed. Clinical disease was detected in only three seroconverters (10%). Incidence Rate of Coccidioidomycosis Infection among Active Duty Stationed at NAS Lemoore, 2011-2017 [Image: see text] Seroconversion Status by Cocci/Pneumonia Diagnosis Status [Image: see text] CONCLUSION: In this study Coccidioides seroincidence was similar to that observed by others, adding longitudinal evidence to epidemiologic assumptions about coccidioidomycosis. A trend toward increasing incidence over the course of the study is consistent with the classification of coccidioidomycosis as an emerging infectious disease. While transmission is typically related to exposure, we did not detect a difference based on military occupational specialty codes. Overall, rates of diagnosed disease in our cohort were lower than the historically-assumed 40% symptomatic rate, although this conclusion is limited by the retrospective nature of the study. Further clinical and epidemiologic coccidioidomycosis research, particularly in broader endemic regions, is warranted. DISCLOSURES: All Authors: No reported disclosures