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Atopic dermatitis (AD) is the most common cutaneous disease in pediatrics, with a high impact on an individual's quality of life, especially in moderate-to-severe cases.1, 2 The epidemiology of AD reports an estimated global prevalence of around 20% in the overall infants (0–5 years old) and children (6–11 years old) population.3 Evidence of the estimated prevalence for the Spanish population of 6–7 years old varies between 3.3%4 to 5.9%5 and 11.5%6 for the age range of 6–12 years old. Our epidemiological study, using a retrospective large-scale population-based database from 2013 to 2017, aims to describe the diagnosed prevalence, comorbidities, and patient population characterization based on hospitalizations, oral corticosteroids (OCS), and immunosuppressants (IS) use in a cohort of patients with AD from 0 to 11 years old from Catalonia (Spain). Inclusion criteria were as follows: (a) Patients aged 0–11 years, and (b) with a diagnosis of AD established by medical records (ICD-9-CM codes 691.8: Other atopic dermatitis and related conditions and 692.9: eczema and contact dermatitis) at any care level covered by the NHS (primary, hospital, and emergency care) at any point in time from January 2013 until December 2017 (follow-up period different for everyone in the dataset). Including the second code might overestimate the prevalence because it includes irritant or allergic contact dermatitis and other non-atopic dermatoses. Notwithstanding, not considering that code would not pick up a consistent number of AD registered in that way. Exclusion criteria were as follows: (a) subjects transferred to other regions in Spain, and (b) permanently institutionalized patients (i.e., patients living in nursing homes, psychiatrists, or other care facilities). Descriptive analysis was conducted by reporting frequencies and proportions of individuals in the overall population, comorbidities, and treatment characteristics. The database information on socioeconomic and demographic factors, which were (1) gender, (2) age, and (3) annual income levels, were constructed and adjusted by household size. Everyone's drug prescription (OCS and IS) and hospitalization over the last 2 years were considered to describe the characteristics of AD infants and children characteristics. Unlike adult and adolescent AD patients, defining severity criteria in infants and children is challenging because AD, despite being considered a chronic disease, in some cases could be resolved. Based on the clinical perspective, it would be more suitable to classify the disease depending on the patient's characterization instead of the severity. Therefore, we decided to further study the description of the severity of the disease in this patient group of infants and children according to these criteria: (1) prescription of IS agents at least one time over the last 2 years; (2) consumption of OCS over the last 2 years; and (3) one or more hospitalizations/emergencies over the last 2 years with AD as a first diagnostic. We decided to use prednisolone as the only OCS because it was used in the highest percentage and the only one available for presentations in the population studied. There were 257,546 infants (119,444) and 138,102 children with an AD diagnosis. The overall diagnosed AD prevalence in the infants and children population was calculated based on all individuals from the study population who received a diagnosis of AD over the total infants and children population in Catalonia (945,191 residents in 2017). Since the database encompasses Catalonia's entire infant and children population, data should be interpreted as the prevalence of those diagnosed in 2017 in Catalonia for those diagnosed from 2013 to 2017. Statistical analyses were conducted using the statistical package Stata 18. The diagnosed prevalence of AD in the population from 0 to 11 years old was 27.2%. By gender, the overall prevalence was higher for females than males (27.7% vs. 26.8%) (Figure 1 and Table S1). The average age was 5.9, and the standard deviation was 3. The overall prevalence was highest for the 6- to 11-year-old group (27.5%). The prevalence for females increases until the highest value (28.6%) for those who were 6–11 years old. In contrast, the prevalence decreases over time for males, being highest (27.2%) for the 0–5 years old (Figure 1). Differences in prevalence between males and females are statistically significant (p < .0001). This is the first Spanish study reporting the overall diagnosed prevalence for an infant and children cohort, in this case, including all individuals in Catalonia from 0 to 11 years old. Another study6 calculated the prevalence for children between 6 and 12 years old (11.5%) with much lower results than in the present study (27.5% for the 6- to 11-year-old children cohort). This could be explained by the use of a smaller sample size (17,533 patients in the 6- to 12-year-old cohort) than in the present study (138,102 patients with 6–11 years old), as well as using more restrictive inclusion criteria, including only those individuals attending a specialist visit, which leads to a much lower prevalence result than in this study and a possible sample bias. Moreover, the present study also includes infants from 0 to 5 years old, with a prevalence of 26.96% not reported elsewhere in Spain for this group of children. More than half (59.4%) of the AD infants and children cohort lived in families with annual incomes <18,000€ (Table S1) based on official Spanish drug copayment cut-off levels. AD comorbidities, including respiratory/allergy and systemic/general, were also analyzed for the general infants and children population and by separate cohorts (Table 1). In line with earlier studies,6, 7 acute bronchitis (40.1%), asthma (9.4%), and allergic rhinitis (5.7%) were the most frequent respiratory/allergic comorbidities, acute bronchitis more frequent in the infant population, and asthma and allergic rhinitis more frequent in the children population. Among systemic comorbidities, overweight (4.4%) was the most prevalent non-respiratory comorbidity, as suggested by the existing literature,6, 8-10 being more frequent in the children cohort (7.0%) (Table 1). Within the 2016–2017 study period and AD infants' population (0–5 years old), 0.89% were prescribed prednisolone, 1.36% were hospitalized, and 0.06% used IS at least once over the last 2 years. In the same period for the AD children population (6–11 years old) compared with the AD infant population (0–5 years old), we noted an increase in prednisolone intake (4.2%), a decrease in hospitalization (0.7%), and an increase in IS intake (0.2%). In the overall AD population (0–11 years old), these figures represent 2.66% (prednisolone), 1.0% (hospitalization), and 0.1% (IS), respectively (Table 2). This study has some limitations. First, the retrospective nature of the research (misclassification and miscoding) and the fact that prescribed medications purchased by the individuals are assumed to be taken to overestimate severe prevalence. Second, we need to determine whether some drugs, such as prednisolone, were prescribed to treat AD or other concomitant diseases. For this purpose, we only included prescriptions close to a recent AD diagnosis in the system. On the contrary, the severity characterization of the AD patients following OCS and IS treatment criteria could also be underestimated by assuming patients with no drug information present a non-severe AD, which might or might not always be the case. Third, the lack of inclusion of individuals diagnosed and treated outside the statutory NHS, in private hospitals or medical centers, could underestimate the prevalence and disease severity results. The current therapeutic scenario, with biological drugs and small molecules approved from 6 months of age, can significantly change the management and prognosis of these patients. In conclusion, this paper aimed to contribute to the literature by providing new evidence using a more significant number of AD patients than previous studies, including richer information on most patients diagnosed with AD from Catalonia's general infants and children population (0–11 years old). Our findings show an overall prevalence of 27.2%, more prevalent for females than males. In our study of the pediatric population, we found hospitalization, OCS, and IS consumption values higher than those of the general population. Moreover, hospitalization criteria are the most common in infants (1.36%) and OCS consumption for children (4.19%). Finally, the most frequent comorbidities were acute bronchitis, asthma, and allergic rhinitis, among the respiratory/allergic conditions. Toni Mora: Investigation; funding acquisition; writing – original draft; methodology; writing – review and editing; software; formal analysis; data curation; project administration. Irene Sánchez-Collado: Software; data curation. Joaquim Mullol: Conceptualization; investigation. Rosa Muñoz-Cano: Conceptualization; investigation. Paula Ribó: Conceptualization; investigation; writing – original draft; methodology; validation; writing – review and editing; supervision. Antonio Valero: Conceptualization; investigation; methodology; supervision. This study was sponsored by the UIC Real-World Evidence Chair (unrestricted grant from SANOFI). All the authors received specific funding for developing this work from the International University of Catalonia (UIC) Real-World Evidence Chair. There are no patents, products in development, or marketed products to declare. The authors of this manuscript have no relevant financial or other relationships to disclose. The peer review history for this article is available at https://www.webofscience.com/api/gateway/wos/peer-review/10.1111/pai.14164. Appendix S1. 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Mora et al. (Wed,) studied this question.