Background/Purpose: We recently developed and validated an index of socioeconomic status (SES) termed HOUSES (HOUsing-based index of SocioEconomic Status) to address unavailability of SES measures in routinely used data sources for clinical research concerning health disparities.  While HOUSES has been associated with various childhood health outcomes, whether HOUSES is associated with adult health outcomes is unknown. Our objective was to assess whether HOUSES (a measure of SES) is associated with risk of and mortality after rheumatoid arthritis (RA).

Methods: We conducted a population-based case-control study among all residents of a geographically-defined area with RA who were identified using 1987 American College of Rheumatology criteria for RA from January 1, 1988 to December 31, 2007.  HOUSES was formulated based on z-score for four real property data (housing value, actual square footage, and numbers of bedrooms and bathrooms) and analyzed in categorical (quartiles) and continuous variables. Self-reported educational level and pertinent risk factors for RA were obtained.  Logistic regression was used to examine the association between HOUSES and risk of RA.  Cox models were used to examine the association between HOUSES and mortality rate during the follow-up after RA adjusting for age, gender, index year of RA, comorbid conditions known to be associated with risk of RA, and therapy for RA.

Results: There were 650 eligible patients who developed RA during the study period and 1:1 matched controls without RA; 604 of RA (93%) and 564 of controls (87%) were successfully geo-coded to real property data. Of these 604 subjects, 418 (69%) were female; the mean age (±SD) was 56±15.6 years, the mean follow-up was 7.7±5.1 years.  HOUSES was associated with risk of developing RA (mean±SD: 0.5±3.8 for controls vs. -0.2±3.1 for RA cases, p=0.003) (odds ratio: 1.06 per 1 unit decrease in HOUSES; 95%CI: 1.02-1.09).  This association persisted after adjustment for smoking status and body mass index. Cumulative mortality rates at 15 years following RA were 33% (95%CI: (27 – 39), 27% (21 – 33), 24% (18 – 30), and 25% (19 – 31) for patients in the first (lowest SES), second, third, and fourth quartiles (highest SES) of the HOUSES index, respectively.  The lowest quartile of HOUSES was significantly associated with increased mortality after RA compared to higher quartiles of HOUSES (HR: 1.74; 95%CI: 1.10-2.74; p-value=0.017) adjusting for RA characteristics, comorbidities and RA therapies.  The association between HOUSES and mortality after RA was not explained by other known risk factors for mortality after RA.  RA therapy such as disease modifying drugs including biologics were not associated with HOUSES nor accounted for the association between HOUSES and mortality after RA.

Conclusion: Lower SES (as measured by HOUSES) is associated with increased risk of RA and mortality after RA.  To reduce the gap in differential mortality after RA among individuals with different SES, clinicians or health care systems need to consider their preventive and therapeutic strategies in the patients’ social context.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/application-of-a-novel-measure-of-socioeconomic-status-using-individual-housing-data-in-rheumatology-research/