Pityriasis rosea: elucidation of environmental factors in modulated autoagressive etiology and dengue virus infection Mehak Singh 1 , Manoj Pawar 2 ✉ , Antonio Chuh 3 , Vijay Zawar 2 1 Department of Dermatology and Venerology, H. B. T. Medical College and Dr. R. N. Cooper Municipal General Hospital, Mumbai, Maharashtra, India. 2 Department of Dermatology, Dr. Vasantrao Pawar Medical College, Nashik, India. 3 Department of Family Medicine and Primary Care, University of Hong Kong and Queen Mary Hospital, Pokfulam, Hong Kong. ✉ Corresponding author: manojpawar624@yahoo.com 15 2019;28:15-20 doi: 10.15570/actaapa.2019.4 Introduction Pityriasis rosea (PR) is suspected to be associated with an infec- tion. However, an exact cause has not been found. Drago et al. reported human herpesvirus 7 to be the causative agent (1). Other investigators reported fndings supporting and refuting such an association. However, the distinct clinical course, a lack of recur- rences in most of the patients, and the presence of temporal case clustering support an infectious etiology. Furthermore, seasonal variation, association with respiratory tract infections, and a his- tory of contact with PR patients in some patients do support an infectious etiology (2). Cluster analysis is a useful approach for elucidating possible infectious etiologies. Several studies have evaluated the presence of clustering in PR (3–12). In 1982, Messenger et al. reported sig- nifcant spatial-temporal clustering only in female patients with PR and a temporal cluster of 16 patients within a 28-day period (3). However, there was no control and the impact of seasonal variation was not studied. Later on, some studies reported sea- sonal variation and/or case clustering for patients with PR (4, 8–11), whereas others did not fnd any signifcant association with seasonal variation and incidence of PR (6, 12). To the best of our knowledge, no study has reported an association of dengue fever with PR. We thus report here a retrospective study investigating the epidemiology of PR and the incidence of dengue fever and its association with PR at a tertiary referral center in Assam. Methods The study was conducted at a tertiary referral center in Guwahati, Assam, India. We searched for and retrieved all medical records of patients diagnosed with PR by dermatologists from December 1st, 2014 to July 31st, 2017. The diagnosis was made only if the patient had fulflled at least three out of the following four clini- cal features: 1) herald patch, 2) peripheral collaret scales, 3) pre- dominant truncal and proximal limb distribution of the lesions, and 4) orientation of lesions along the lines of cleavage. These diagnostic criteria were laid down and validated by us (13, 14). For each visit by every patient, we retrieved data for the monthly mean air temperature, mean total rainfall, and mean relative hu- midity. PR patients that had dengue fever were studied along with healthy controls. The detection of NS1 antigen was done using the Panbio Dengue Early enzyme-linked immunosorbent assay (ELI- SA) (Inverness Medical Innovations, Australia). The detection of IgM antibodies was done using the Dengue-IgM capture ELISA kit (National Institute of Virology, Pune). IgG anti-dengue antibodies were detected using the dengue IgG capture ELISA (PanBio Pty Ltd, Queensland, Australia). The following steps were used for the statistical analysis: a) 2 × 2 contingency tables were drawn to calculate the odds ratio (OR) and risk ratio (RR), as well as a chi-square test, and fnally a two-tailed Fisher’s exact test (p < 0.05 was con- sidered statistically signifcant); Abstract Introduction: A retrospective epidemiological study was conducted to study seasonal variation in the incidence of pityriasis rosea (PR) and its temporal association with various meteorological variables, and dengue virus infection. Methods: The study was conducted at a tertiary referral center in Guwahati, Assam, India. We searched for and retrieved all medi- cal records of patients diagnosed with PR by dermatologists from December 1st, 2014 to July 31st, 2017. The diagnosis was made only if the patient fulflled at least three out of the following four clinical features: 1) herald patch, 2) peripheral collaret scales, 3) predominant truncal and proximal limb distribution of the lesions, and 4) orientation of lesions along the lines of cleavage. For each visit by every patient, we retrieved data for the monthly mean air temperature, mean total rainfall, and mean relative humidity. PR patients that had dengue fever with NS1 antigen and/or IgM/IgG antibody positivity were studied along with healthy controls. Results: Overall, PR occurred more frequently in the colder months and months with less rainfall. However, these associations were insignifcant (p = 0.23, R = −0.38, and R = −0.55, respectively). Upon further examination of the data, we found that the monthly incidence of PR was signifcantly lower in March and April than the other months during the study period (F = 8.31, p = 0.002). A statistically signifcant higher incidence was detected in September, November, and December (p < 0.01 for 2014 and 2017, but not in the 2016 seasonal cohort) and also in January and February (p < 0.05 for 2016 and 2017). Interestingly, a retrospec- tive history of dengue fever emerged as a signifcant correlate. Conclusions: In our setting, there was signifcant temporal clustering and seasonal variation among patients with PR. The inci- dence of dengue fever is signifcantly correlated with PR. Keywords: dengue, pityriasis rosea, seasonal variation Acta Dermatovenerologica Alpina, Pannonica et Adriatica Acta Dermatovenerol APA Received: 18 August 2018 | Returned for modifcation: 6 December 2018 | Accepted: 25 December 2018