Editorial: Updates in US systemic lupus erythematosus epidemiology: Tales of two cities.

While contemporary US and international systemic lupus erythematosus (SLE) consortia (1–3) have greatly advanced our knowledge regarding the disease, many argue that such registries suffer from referral bias and do not accurately represent the spectrum of disease at the population level. In contrast, population-based cohort studies encompass the spectrum of mild through severe cases of SLE and can estimate incidence and prevalence. Yet identifying the full range of cases for this disease across a given population requires multiple data sources with precisely interpreted clinical, laboratory, and even pathology data. These factors have made SLE one of the most challenging diseases to research through epidemiologic or administrative data (4). Moreover, the few existing US population-based SLE cohorts summarized in a 2009 review (5) are now largely outdated or had described SLE prevalence and incidence rates in small, homogeneous, geographic regions (6,7). Those studies reported widely varying rates of SLE, likely related, at least in part, to differences in methodology. Updating contemporary lupus population-based epidemiology is critically important to framing the current public health burden and status of SLE care in the US. SLE is a disease with substantial direct and indirect costs over the patient’s lifespan (8,9) and with well-known health disparities. Important health disparities, including higher renal complications and mortality rates, have been noted in groups defined by low socioeconomic status, black race, Hispanic ethnicity, or Asian ethnicity (1,3,10–12). Prior reports from US referral cohorts representing some of these vulnerable populations are criticized for missing mild cases and patients with limited access to care. To include such cases, it is important to have a broad definition of case ascertainment and to search multiple points of entry into the health care system, ranging from tertiary centers to community clinics and hospitals, or even laboratory and pathology services. To date, the lack of a comprehensively defined population-based “denominator” to accurately represent the number of SLE cases in the US has limited our ability to answer many important questions. For example, without accurate numbers of existing SLE cases, it has been difficult to adequately quantify the burden of SLE in the US, let alone reassess health disparities and SLE quality of care on a population level (13). Two reports in this issue of Arthritis & Rheumatology, one by Lim et al (14) and the other by Somers et al (15), describe collaborative studies offering muchneeded updates on the epidemiology of SLE in the US. Among the key contributions of their work are the pivotal partnerships with the Centers for Disease Control and Prevention (CDC) and their respective state health departments. These groups cooperated under a state public health surveillance exemption to Health Insurance Portability and Accountability Act (HIPAA) to facilitate comprehensive regional searches for SLE cases. Both groups of investigators ascertained all pediatric and adult cases of SLE encountered between 2002 and 2004 in hospitals, dermatology, nephrology, and rheumatology clinics, pathology and laboratory centers, and the US Renal Data System for end-stage renal disease (ESRD). The results of these two studies were derived from two comparable urban populations, Atlanta and Detroit and their surrounding areas, and they provide contemporary data on SLE incidence and prevalence in these regions. These rigorous studies update the epidemiologic data on SLE with improved precision, highlighting the magnitude of the disease burden, including important health disparities for SLE patients. Using parallel methods, Lim (14) and Somers (15) found nearly identical SLE rates of 5.6 versus 5.5 incident SLE cases per Dr. Bartels’ work was supported by the NIH (National Institute of Arthritis and Musculoskeletal and Skin Diseases grant K23-AR-062381). Christie Michels Bartels, MD, MS: University of Wisconsin, Madison; Rosalind Ramsey-Goldman, MD, DrPH: Northwestern University, Feinberg School of Medicine, Chicago, Illinois. Address correspondence to Christie Bartels, MD, MS, Department of Medicine, Rheumatology Division, University of Wisconsin, 1685 Highland Avenue, Room 4132, Madison, WI 53705-2281. E-mail: [email protected]. Submitted for publication October 3, 2013; accepted in revised form October 15, 2013.