Lee, AlbertAlbertLeeChuh, A. A. T.Molinari, N.2026-05-052026-05-052003https://repository.sfu.edu.hk/handle/sfu/5384<b>Objectives</b> To investigate the epidemiology of pityriasis rosea in primary care settings in Hong Kong and to analyze for temporal clustering. <b>Design</b> Retrospective epidemiologic study. <b>Setting</b> Six primary care teaching practices affiliated with a university. <b>Patients</b> Forty-one patients with pityriasis rosea, 564 patients with atopic dermatitis (negative control condition), and 35 patients with scabies (positive control condition). <b>Methods</b> We retrieved all records of patients with pityriasis rosea, atopic dermatitis, or scabies diagnosed in 3 years. We analyzed temporal clustering by a method based on a regression model. <b>Results</b> The monthly incidence of pityriasis rosea is negatively but insignificantly correlated with mean air temperature (γs = −0.41, P = .19) and mean total rainfall (γs = −0.34, P = .27). Three statistically significant clusters with 7, 6, and 7 cases were identified (P = .03), occurring in the second coldest month in the year (February), the second hottest month (July), and a temperate month (April), respectively. For atopic dermatitis (negative control condition), the nonclustering regression model was selected by Akaike information criteria. For scabies (positive control condition), 1 cluster of 20 cases was detected (P = .03). <b>Conclusions</b> Significant temporal clustering independent of seasonal variation occurred in our series of patients with pityriasis rosea. This may be indicative of an infectious cause.enjournal article10.1001/archderm.139.4.489