Background/Purpose: Coccidioidomycosis (Cocci) is a fungal infection endemic to seven states in the US. Biologic response modifiers (BRMs) have been shown to increase the risk of serious infections including fungal infections, but data are limited on the risk of Cocci with BRMs and corticosteroids (CSTs). Our objective was to examine the association between use of DMARDs, BRMs, and CSTs and subsequent risk of Cocci infection among Medicare beneficiaries with rheumatic or autoimmune diseases.

Methods: In a retrospective cohort study using 2011-2013 Medicare claims data (5% representative sample), we restricted the analyses to continuously enrolled, fee-for-service beneficiaries who resided in Arizona, California, New Mexico, Nevada, Texas, Utah, and Washington. Among beneficiaries having any of ten rheumatic/autoimmune diseases (i.e., RA, SLE, psoriasis, PsA, AS, PM, DM, IBD, ReA, and SSc), we identified those who initiated DMARDs, BRMs, CSTs or did not use any DMARDs/BRMs/ CSTs. The index date was defined as the earliest date of the rheumatic/autoimmune disease diagnosis or first prescription of CSTs, DMARDs, or BRMs. Individuals with diagnosed Cocci infection prior to the index date were excluded. Based on the refill days supplied, we created time-varying exposure variables of DMARDs, BRMs, and CSTs, and applied a 90 day lag period following drug cessation. We used multivariable Cox proportional hazard regression to examine DMARD, BRM, and CSTs use and the risk of subsequent Cocci infection, adjusted for age, sex, race, Medicaid eligibility, low income subsidy, RxHCC risk score, Elixhauser comorbidity index, disability, metropolitan area, opioid use, and NSAID use within 3 months of the index date. Cox models included indicator variables for CSTs, DMARDs, and BRMs simultaneously.

Results: Among 14,931 beneficiaries (mean age: 68.7; white: 75.3%, black: 7.6%), 51 individuals were diagnosed with Cocci during the study period (1.6 per 1,000 person-years). Increased risk of Cocci was observed among beneficiaries prescribed any CSTs (HR=1.94, 95%CI: 1.10, 3.42) and any BRMs (HR=2.25, 95%CI: 1.02, 4.95), though not for individuals prescribed any DMARDs (HR=1.02; 95%CI: 0.54, 1.91), seen in Table 1.

Conclusion: The overall incidence of Cocci was low among Medicare beneficiaries with rheumatic or autoimmune diseases in the southwestern United States from 2011 to 2013. Our findings suggest that BRM and CSTs users may have higher risk of Cocci compared to non-users, but no evidence of increased risk was observed for those who used DMARDs. Cocci is a serious infection, and warrants consideration for regular screening among clinicians for individuals on BRMs and CSTs.