Purpose of Review The epidemiology of antiphospholipid syndrome (APS) is poorly understood. Here, we review the current understanding of the epidemiology of antiphospholipid syndrome in the general population and the frequency of antiphospholipid antibodies in the general population in patients with obstetric morbidity, arterial events, and venous thromboembolism. Recent Findings There have been few population-based studies that estimated the prevalence and incidence of APS. The estimated incidence and prevalence among most these studies ranged between 1 and 2 cases per 100,000 and 40 and 50 cases per 100,000 respectively. The prevalence of antiphospholipid antibodies in patients with obstetric morbidity was 6–9%, while in arterial events and venous thromboembolism is 9–10%. However, this data remains limited. Mortality of patients with APS is 50–80% higher than the general population. Summary The epidemiology of APS has been difficult to elucidate. Population-based studies patients with diverse age, racial, and ethnic backgrounds are needed.

ObjectivesTo determine the trends in incidence, prevalence and mortality of systemic lupus erythematosus (SLE) in a US population over four decades.MethodsWe identified all the patients with SLE in Olmsted County, Minnesota who fulfilled the European Alliance of Associations for Rheumatology (EULAR)/American College of Rheumatology (ACR) criteria for SLE during 1976–2018. Age-specific and sex-specific incidence and prevalence dates were adjusted to the standard 2000 projected US population. The EULAR/ACR score was used as a proxy for disease severity. Standardised mortality ratio (SMR) was estimated.ResultsThere were 188 incident SLE cases in 1976–2018 (mean age 46.3±SD 16.9; 83% women). Overall age-adjusted and sex-adjusted annual SLE incidence per 100 000 population was 4.77 (95% CI 4.09 to 5.46). Incidence was higher in women (7.58) than men (1.89). The incidence rate increased from 3.32 during 1976–1988 to 6.44 during 2009–2018. Incidence rates were higher among the racial and ethnic minority populations than non-Hispanic whites. The EULAR/ACR score did not change significantly over time. Overall prevalence increased from 30.6 in 1985 to 97.4 in 2015. During the study period, there was no improvement in SMR over time (p=0.31).ConclusionsThe incidence and prevalence of SLE are increasing in this US population. The increase in incidence may be at least partially explained by the rising ethnic/racial diversity of the population. There was no evidence that the severity of SLE has changed over time. The survival gap between SLE and the general population remains unchanged. As the US population grows more diverse, we might continue to see an increase in the incidence of SLE.

Objective To estimate the incidence and time-to-classification of systemic lupus erythematosus (SLE) by the 1997 American College of Rheumatology (ACR97) criteria, the Systemic Lupus International Collaborating Clinics (SLICC) criteria, and the European Alliance of Associations for Rheumatology/American College of Rheumatology (EULAR/ACR) criteria. Methods We identified all incident SLE cases from 2000–2018 in the well-defined Olmsted County population. Clinical data included in the ACR97, SLICC and EULAR/ACR criteria were manually abstracted from medical records. All incident cases met at least one of the 3 classification criteria. Time-to-classification was estimated from the first documented lupus-attributable disease manifestation to the time of criteria fulfillment by each of the three definitions. Annual incidence rates were age or age/sex adjusted to the 2000 US population. Results Of 139 incident cases there were 126 cases by the EULAR/ACR criteria, corresponding to an age/sex-adjusted incidence of 4.5 per 100 000 population (95% CI, 3.7–5.2). The age/sex-incidence was higher than that of the SLICC criteria (113 cases; 4.0 per 100 000 [95%CI, 3.3 – 4.7], p= 0.020) and the ACR97 (92 cases; 3.3 per 100 000 [95%CI 2.6–3.9], p< 0.001). The median time from first disease manifestation to criteria fulfillment was shorter for the EULAR/ACR criteria (29.4 months) than the ACR97 criteria (47.0 months, p< 0.001) and similar to the SLICC criteria (30.6 months, p= 0.83). Conclusion The incidence of SLE was higher by the EULAR/ACR criteria compared with the ACR97 and the SLICC criteria, and the EULAR/ACR criteria classified patients earlier that the ACR97 criteria but similar to the SLICC criteria.