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Previous assessments of the prevalence of lupus were conducted in short periods of time, therefore limiting the insight into long-term trends and potential explanations for the observed patterns.
Over the past 4 decades, the incidence and prevalence of systemic lupus erythematosus (SLE) have increased within the US population, due in part to rising ethnic and racial diversity of the population. However, the severity of SLE symptoms and the survival gap between SLE and the general population have not changed, according to a study published in Annals of Rheumatic Diseases.1
“The Centers for Disease Control and Prevention (CDC) five surveillance registries have provided estimates regarding the incidence and prevalence of SLE across different racial and ethnic groups,” investigators explained. “These registries have confirmed that SLE is more frequent in racial and ethnic minority populations compared with the white population. Prior studies have reported discrepant results regarding the incidence trends of SLE, some reporting an increase while others reporting a decrease in SLE incidence. However, case ascertainment has been conducted in short periods of time, thus not providing long-term trends. In addition, prior studies have not explored potential explanations for the observed trends.”
In the population-based study, adult patients with SLE in Olmsted County, Minnesota were evaluated for age- and sex-specific incidence and prevalence using data from the Rochester Epidemiology Project (REP). Eligible patients met the European Alliance of Associations for Rheumatology (EULAR)/American College of Rheumatology (ACR) criteria for SLE between January 1976 and December 2018. Information including sex, age, race and ethnicity, clinical data, estimated SLE damage index 2000 (SLEDAI-2K), vital stats, disease characteristics, diagnosis date, and date of last follow-up was collected. Incidence and prevalence dates were adjusted to the standard 2000 projected US population. The EULAR/ACR score was used to determine disease severity. Mortality rates were estimated via Kaplan-Meier methods and compared with survival rates of the general population.
A total of 188 incident cases of SLE were identified (mean age of 46.3 years, 83% women). Age- and sex-adjusted incidence per 100,000 people was 4.77 (95% CI 4.09 to 5.46). Unsurprisingly, incidence was higher in women (7.58, 95% CI 6.38 to 8.78) when compared with men (1.89, 95% CI 1.23 to 2.55) and higher in racial and ethnic minority populations when compared with non-Hispanic Whites.
Incidence rates increased from 3.32 (95% CI 2.03 to 4.60) from 1976 through 1988 to 6.44 (95% CI 4.97 to 7.91) from 2009 through 2018 per 100,000 people. Prevalence increased from 30.6 in 1985 to 97.5 in 2015. Between 1999 and 2018, the overall incidence rate for SLE in non-Hispanic Whites was 5.42 (95% CI: 4.34 to 6.51) compared with 8.17 (95% CI: 5.04 to 11.30) in racial and ethnic minorities.
Analyzing cases over 40 years allowed investigators to understand the epidemiology of SLE and how it has changed in the long-term. Misclassification was minimized by using the EULAR/ACR classification criteria and detailed medical record review. However, its retrospective nature limited the study as it was reliant on medical records to determine cases. Further, as the EULAR/ACR score requires a positive ANA, patients with ANA-negative lupus may have been excluded. However, only 4% of the Systemic Lupus Erythematosus International Collaborating Clinics (SLICC) cohort were ANA-negative, so it presumably did not have a major impact on estimates. Finally, as the data was based in a single US county, results may not be generalizable to more diverse regions.
“The results of this population-based study showed that in this US population the incidence and prevalence of SLE is increasing,” investigators concluded. “As the US population grows more diverse, we might continue to see an increase in the incidence of SLE.”
Duarte-García A, Hocaoglu M, Valenzuela-Almada M, et al. Rising incidence and prevalence of systemic lupus erythematosus: a population-based study over four decades [published online ahead of print, 2022 May 16]. Ann Rheum Dis. 2022;annrheumdis-2022-222276. doi:10.1136/annrheumdis-2022-222276