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Annals of Medicine and Medical Education
Volume 2, Issue 3 (November 2015), pp. 57-64

DOI: 10.12973/ejms.2015.144p

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Research Article

Published online on Nov 01, 2015

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Assessing Effect of Infection in Each Season of the Year on Recurrence of Psoriasis: Using the Time-Dependent Coefficient Rates Model for Recurrent Event Data

Freshteh Osmani, Ebrahim Hajizadeh & Parvin Monsouri


Psoriasis can be provoked or exacerbated by a variety of different environmental factors, particularly infections. This disease may occur frequently for a person. Therefore, it's placed in recurrent event category. Unfortunately, few studies have determined which factors are independently associated with psoriasis. We attempted to provide an estimate of the risk for psoriasis associated with a recent infectious disease in different seasons of year and to explore other potential risk factors. The current study was conducted at the Department of Dermatology, Imam Khomeini Hospital, Tehran University of Medical Sciences, between March 2006 and April 2014. A total of 160 patients with confirmed diagnosis of psoriasis were included in the analysis. The original outcomes of the study were recurrent event times. Time dependent rate model was applied to assess the estimate of the effect of infection in different seasons association with psoriasis recurrence and also investigate other affective factors. Up to 6 recurrences were observed during the study time, but only 10% of the patients experienced more than 3 recurrences. The results showed positive correlation between the impact of infection in cold weather and recurrence of psoriasis (P < 0.001).The risk increased with the reported history of any infectious disease. According to the results of model fitting, the impact of infection on recurrence of psoriasis was significantly different in different seasons, so that patients who had infections faced with a higher recurrence risk during the winter (P < 0.01). The patients with types of infections were more likely to experience psoriasis recurrence especially in the winter. Therefore it can be concluded that changes of season of year infections even streptococcal infection in cool weather may provide the progression of the psoriasis and the hazard of its recurrence. 

Keywords: psoriasis, recurrent event, infection, time-dependent coefficient rates model

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