Background/Purpose: The incidence of systemic lupus erythematosus (SLE) varies significantly across patients from different racial/ethnic backgrounds, and is highest in non-Caucasian populations.  In addition, poverty has been associated with increased SLE severity and mortality, independent of race/ethnicity. How the incidence of SLE varies by income level, the main determinant of poverty, is unknown. 

Methods: Using OptumLabs Data Warehouse, a large administrative database of commercially insured and Medicare Advantage beneficiaries, we identified adults with newly diagnosed SLE (ascertained using three ICD-9/10 codes at least 30 days apart) from 2013-2017. Patients had at least two years of enrollment prior to SLE diagnosis. Patients of ≥65 years were excluded due to difficulty in estimating income after retirement. Income was based predominately on self-report or when data were missing, derived rule sets were used. Income was missing in 5% of the sample. We estimated the incidence rate (IR) of SLE per 100,000 person-years stratified by income and racial/ethnic categories with age- and sex-adjusted adjustment to the 2010 US total population aged 18-64 years.

Results: We identified 2810 patients with newly diagnosed SLE. The average age (SD) was 44.9 (12.5), 62% of the patients were Caucasian, 16% Black, 15% Hispanic, 7% Asian/other, and 88% were female.  The overall age-, sex- and race/ethnicity-adjusted IR was 3.4 (95% confidence interval: 3.3-3.5) per 100,000. SLE incidence was 8 times higher among women (9.1) than men (1.2). The incidence rate among Blacks was twice as high as that of Caucasians, and was moderately higher in Hispanic and Asian/other compared to Caucasians. SLE incidence was 12% higher in those with <$40,000 household income than those with ≥$40,000 income. Caucasians with <$40,000 income had 20% higher SLE incidence than those with ≥$40,000 income, but there was no evidence of a differential income effect among minorities  

Conclusion: The incidence of SLE is highest among Blacks, and Hispanics.  Lower income is associated with higher incidence of SLE in Caucasians; this differential effect of income on disease incidence was not seen in minorities.

Table. Incidence Rates of SLE per 100,000 person years according to income