How many people are affected by systemic lupus erythematosus ?
For unknown reasons, in industrialized Western countries SLE has become 10 times more common over the past 50 years. While estimates of its prevalence vary, SLE is believed to affect 14.6 to 68 per 100,000 people in the United States, with females developing SLE more often than males. It is most common in younger women; however, 20 percent of SLE cases occur in people over age 50. Because many of the signs and symptoms of SLE resemble those of other disorders, diagnosis may be delayed for years, and the condition may never be diagnosed in some affected individuals.  In industrialized Western countries, people of African and Asian descent are two to four times more likely to develop SLE than are people of European descent. However, while the prevalence of SLE in Africa and Asia is unknown, it is believed to be much lower than in Western nations. Researchers suggest that factors such as ethnic mixing, tobacco use in industrialized countries, and the different types of infections people acquire in different regions may help account for the discrepancy. For example malaria, which occurs often in tropical regions, is thought to be protective against SLE, while the Epstein-Barr virus, more common in the West, increases SLE risk.