Prevalence and incidence of systemic lupus erythematosus in a population-based registry of American Indian and Alaska Native people, 2007-2009

Abstract

Objective: Few studies have investigated the epidemiology of systemic lupus erythematosus (SLE) in American Indian and Alaska Native populations. The objective of this study was to determine the prevalence and incidence of SLE in the Indian Health Service (IHS) active clinical population in 3 regions of the US.

Methods: For this population-based registry within the IHS, the denominator consisted of individuals in the IHS active clinical population in 2007, 2008, and/or 2009 and residing in a community in 1 of 3 specified regions. Potential SLE cases were identified based on the presence of a diagnostic code for SLE or related disorder in the IHS National Data Warehouse. Detailed medical record abstraction was performed for each potential case. The primary case definition was documentation in the medical record of ≥4 of the revised American College of Rheumatology criteria for the classification of SLE. Prevalence was calculated for 2007, and the mean annual incidence was calculated for the years 2007 through 2009.

Results: The age-adjusted prevalence and incidence of SLE according to the primary definition were 178 per 100,000 person-years (95% confidence interval [95% CI] 157-200) and 7.4 per 100,000 person-years (95% CI 5.1-10.4). Among women, the age-adjusted prevalence was 271, and the age-adjusted incidence was 10.4. The prevalence was highest in women ages 50-59 years and in the Phoenix Area IHS.

Conclusion: The first population-based lupus registry in the US American Indian and Alaska Native population has demonstrated that the prevalence and incidence of SLE are high. Our estimates are as high as or higher than the rates reported in the US black population.

Figure 1

Flow diagram for inclusion of potential cases in the population-based systemic lupus erythematosus (SLE) registry in the US American Indian and Alaska Native population. The denominator for each region represents the active clinical population in 2007 for the communities of interest included in the registry. Potential cases in the denominator identified as having an International Classification of Diseases, Ninth Revision code associated with lupus or other connective tissue disease were flagged for medical record abstraction. Potential cases are classified as either not validated (includes miscoded cases, alternate diagnoses, and insufficient American College of Rheumatology [ACR] criteria for classification as SLE) or validated (documentation in the medical record of ≥4 of the ACR classification criteria for SLE). Validated cases are subdivided into prevalent cases (2007) or incident cases (2008–2009). Incident cases in 2007 were included in the number of prevalent cases in 2007 (*).

Figure 2

Age-specific prevalence of systemic lupus erythematosus (SLE) based on the primary definition (documentation in the medical record of ≥4 of 11 American College of Rheumatology classification criteria for SLE) by region and overall, in women (A) and men (B).