Prevalence and incidence of chronic spontaneous urticaria in the entire Korean adult population

Dear Editor, Ethnic differences and temporal trends in the epidemiology of chronic spontaneous urticaria (CSU) are not well understood, especially in East Asia.1,2,3 The aim of our study was to investigate trends in the prevalence and incidence of CSU among adult Korean patients from 2006 to 2014 using a nationwide, population‐based study. This study used the national health claims database established by the National Health Insurance Service of Korea, which covers nearly the entire Korean population. The study protocol was approved by the Institutional Review Board of Seoul St Mary's Hospital, The Catholic University of Korea (KC16EISE0852). Data from all Koreans aged ≥ 20 years from 2003 to 2015 were included in this study. Diagnosis of CSU was based on the International Classification of Diseases, 10th Revision, Clinical Modification codes. We defined a diagnosis of CSU when one of the following two criteria and a prescription criterion were met: either (i) two outpatient diagnoses of L50.1 (idiopathic urticaria), L50.8 (other specified urticaria) or L50.9 (urticaria, unspecified) at least 6 weeks apart within 1 year; or (ii) one outpatient diagnosis of L50.1, L50.8 or L50.9 plus one diagnosis of T78.3 (angioneurotic oedema) at least 6 weeks apart within 1 year. This definition was validated to have a positive predictive value of 90·4% and a sensitivity of 71·1%.4 The date of prior diagnosis was considered as the date of CSU diagnosis. To improve diagnostic accuracy, we added a prescription criterion: a prescription lasting ≥ 42 days of an antihistamine under the diagnosis of L50.1, L50.8 or L50.9 within 1 year of the initial diagnosis. We included diagnosis by both general practitioners and specialists from primary‐care clinics to referral hospitals. The annual prevalence was calculated as the number of patients with prevalent CSU divided by the total population each year from 2006 to 2014. Patients within 1 year after the date of CSU diagnosis were considered as having prevalent CSU. The annual incidence was calculated as the number of patients with newly diagnosed CSU each year from 2006 to 2014 divided by the number of people at risk each year (individuals who were not diagnosed with CSU before each year). The prevalence and incidence were weighted to reflect the age distribution. Age‐adjusted prevalence and incidence are presented as percentages and per 1000 person‐years, respectively. Table 1 shows the annual age‐adjusted prevalence and incidence of CSU in the study population from 2006 to 2014. The annual age‐adjusted prevalence of CSU was in the range of 0·16–0·45%. The annual age‐adjusted incidence of CSU was in the range of 1·02–2·43 per 1000 person‐years. In each year, women had a higher prevalence and incidence than men. Annual age‐adjusted prevalence and incidence of chronic spontaneous urticaria (CSU) in the study population from 2006 to 2014 Annual age‐adjusted prevalence and incidence of chronic spontaneous urticaria (CSU) in the study population from 2006 to 2014 The prevalence in our study (0·16–0·45%) was comparable with those in previous studies in Taiwan (0·69–0·79%),1 Italy (0·02–0·38)5 and the U.S.A. (0·08%6 and 0·11%),7 although our study and previous studies were different in the study methodologies and study populations. To our knowledge, only one previous study measured the longitudinal prevalence and incidence of CSU using a nationwide database: a study from Italy reported that the annual prevalence and incidence of CSU from 2002 to 2013 ranged from 0·02% to 0·38% and 0·10 to 1·50 per 1000 person‐years, respectively.5 However, that study did not present an age‐adjusted rate, but rather a crude one, and it included patients from general practitioners only. Except for particularly low rates in 2002–2003, the reported Italian prevalence and incidence rates were similar to our results, and showed steady trends from 2004 to 2013.5 A Taiwanese nationwide population‐based study of chronic urticaria also showed steady trends of prevalence ranging from 0·69% to 0·79%, and an incidence of around 0·50% from 2009 to 2012.1 In contrast to previous studies, the prevalence and incidence of CSU in our study consistently increased annually from 2006 to 2014 (2·81‐fold and 2·38‐fold during 8 years, respectively). These trends could be influenced by several factors, including improved rates of survival, demographic changes and diverse environmental and behavioural factors. We suspect that recent rapid socioeconomic growth and changes towards a Western lifestyle in Korea might contribute to this increasing trend. Better disease awareness and medical service accessibility for patients with CSU also contributed. Because CSU carries a substantial quality‐of‐life impairment and economic cost, the increasing prevalence and incidence of CSU could cause a substantial disease burden and should be further investigated.8 Limitations of our study were the definition of CSU based on disease codes and unavailable information on over‐the‐counter medications. However, our study includes the largest number of patients with CSU to date. In conclusion, we present the longitudinal prevalence and incidence of CSU in the entire adult Korean population, where we found increasing trends. Our results could expand knowledge about the epidemiology and disease burden of CSU. This study used data collected by the National Health Insurance Service (NHIS‐2016‐1‐145). Funding sources: none. Conflicts of interest: none to declare