Estimating the Prevalence of Systemic Sclerosis in the Lorraine Region, France, by the Capture–recapture Method

ObjectiveTo assess the prevalence of systemic sclerosis (SSc) in the Lorraine region, France.MethodsData from three sources – general practitioners and community and hospital specialists, medical records departments, and regional and national laboratories−and a capture–recapture method with log-linear models were used to estimate SSc prevalence in the region. Double recording was checked, and reported cases were validated after a review of medical records.ResultsWe identified 560 records of suspected SSc cases corresponding to 327 unique suspected SSc cases existing on June 30, 2006, in Lorraine. On the basis of the 193 validated cases (22 [11.4%] with diffuse disease, 136 [70.5%] with limited disease, 31 [16.1%] with limited involvement and 4 unknown), the observed overall crude prevalence of SSc was 105.4 cases per million adult inhabitants (95% confidence interval [CI]: 91.0; 121.4). With the capture–recapture method, the estimated number of SSc cases was 233 (95% CI: 217.3; 260.0), so an estimated 40 cases were not identified by the three sources. The estimated overall prevalence was 132.2 cases per million adult inhabitants (95% CI: 115.8; 154.0).ConclusionsOur study provides the first estimate of SSc prevalence in the Lorraine region. The capture–recapture method allowed us to estimate an additional 21% of unobserved cases and is a good alternative to the community-based study design for estimating the prevalence of rare diseases.