Epidemiology of systemic lupus erythematosus in rural Wisconsin.

We investigated the epidemiology of systemic lupus erythematosus (SLE) in the Marshfield Epidemiologic Study Area (MESA), a defined rural region where nearly all residents obtain their health care from a large clinic system. Computerized medical records were searched to identify MESA residents diagnosed with SLE from 1991 through 2001. Medical records were manually reviewed for all selected patients to identify cases of SLE using the 1982 revised American College of Rheumatology criteria. Patients with > or = 4 criteria were classified as definite SLE. Age- and gender-specific SLE incidence rates (1991-2001), the population prevalence rate of SLE on 31 December 2001 and survival rates were calculated. We identified 117 MESA residents with definite SLE. The average age-adjusted incidence of definite SLE was 5.1 per 100 000 per year (95% CI: 3.6, 6.6) and the age-adjusted population prevalence was 78.5 per 100 000 (95% CI: 59.0, 98.0). The mean age at diagnosis among the 44 incident cases was 51.7 years (range: 14-90 years). Positive anti-nuclear antibody (ANA), hematologic abnormalities, arthritis and renal disease were common at diagnosis. Five- and 10-year survival rates were 88% and 76%, respectively. Epidemiologic characteristics of SLE in this rural Caucasian population are generally similar to those reported by other US studies. One notable difference is a relatively high incidence of SLE in older adults.