Incidence and prevalence
There are significant racial and gender differences in the incidence and prevalence of PS, with higher rates apparent in women than men. The American Thoracic Society (ATS) has reported that the incidence and prevalence are highest in African Americans and Nordic countries.
The ATS has estimated that the number of cases/year is 36/100,000 in African Americans, compared with 11/100,000 in Caucasian Americans.
Geographical location has been identified as an important factor. For example, the incidence per 100,000/year in Sweden and France is 12 and 5, respectively, while the prevalence per 100,000 in these two countries is 160 and 30, respectively.