Atopic dermatitis (AD), also known as atopic eczema, eczema, endogenous eczema, and neurodermatitis, is a chronic inflammatory skin disease occurring in children, adolescents, and adults. Patients with AD often have severe itching and may have other atopic diseases (e.g., allergic rhinitis, asthma, or allergic conjunctivitis). AD has a profound impact on patients’ quality of life. The prevalence of AD in Chinese children has been reported.[1] However, no large-scale population-based study has focused on the prevalence of AD in Chinese adults. The present nationwide survey was conducted to investigate the prevalence and risk factors of AD in Chinese adults. This study received ethics approval of Peking University People's Hospital (No. 2017PHB074-01). Informed consent was obtained from all participants. This cross-sectional survey was conducted in 35 cities of 31 provinces in China from July to December 2017. The pre-estimated sample size was approximately 35,000. The estimated sample size in each region was calculated according to the geographic distribution in the National Census 2010. The cluster sampling method was adopted. Two to three communities in each city were randomly selected for this on-site investigation. Adult residents were invited to complete the questionnaires and undergo a dermatological examination. People with severe diseases or cognitive, linguistic, or mental disorders were not included. The investigators were dermatologists from Peking University People's Hospital and local medical college hospitals. All were trained for this investigation and required to pass an examination for qualification. AD was defined as a clinical diagnosis of AD, eczema, or neurodermatitis by dermatologists. The 1-year prevalence of AD was defined as having clinical manifestations of AD during the past 12 months. The point prevalence was defined as having AD upon dermatological examination. Current smokers were defined as having smoked daily during the past 12 months, ex-smokers as having stopped smoking for at least 1 year before the survey, and non-smokers as having never smoked. The severity of AD was determined by the Severity Scoring of Atopic Dermatitis (SCORAD) index. The age- and sex-adjusted prevalence of AD was calculated based on the China Population Composition in 2010. All data were input using EpiData 3.1 (EpiData Association, Odense, Denmark), and statistical analyses were performed with SPSS 22.0 (IBM Corp., Armonk, NY, USA). Quantitative data are presented as mean and standard deviation, whereas qualitative data are presented as number and/or percentage. Differences in the partici-pants’ characteristics between groups were evaluated using the student's t test for quantitative variables and the chi-squared test for categorical variables. Differences in the prevalence of AD between regions were compared by logistic regression models adjusted by age and sex. Logistic regression models that included significant variables identified in the chi-squared tests were constructed to identify risk factors for AD. Crude and adjusted odd ratios and 95% confidence intervals (CIs) were calculated. P values of <0.05 were considered significant. A total of 44,875 questionnaires were distributed and 40,573 were collected (response rate, 90.41%). After quality control selection, 36,700 valid questionnaires were finally included. The study population comprised 15,853 (43.20%) men and 20,847 (56.80%) women ranging from 18.0 to 99.0 years of age (mean, 35.58 ± 15.65 years). The 1-year prevalence of AD was 6.00% (95% CI, 5.76%–6.24%). After age- and sex-standardization, the prevalence was 6.13%. Women had a higher prevalence than men (6.38% vs. 5.50%, P < 0.001), with an adjusted prevalence of 6.48% and 5.80%, respectively. The prevalence of AD was similar across different age groups. The prevalence of AD in different regions ranged from 5.49% to 6.72%, as shown in [Supplementary Table 1, https://links.lww.com/CM9/B405]. The prevalence of AD was higher in urban areas than in rural areas (6.31% vs. 2.58%, P < 0.001). The point prevalence of AD was 2.17% (95% CI, 2.02%–2.32%) (2.13% in men and 2.20% in women, P = 0.664). After standardization, the point prevalence of AD was 2.42% (2.39% in men and 2.46% in women). The lesions of AD were most common on the hands (24.28%), followed by lower legs (21.51%), neck (21.38%), and face (14.97%). Mild, moderate, and severe AD was present in 73.33%, 24.78%, and 1.89% of patients, respectively, based on the SCORAD index. Of all patients, 66.08% experienced the first onset after 18 years of age. Self-reported food allergy and drug allergy were found in 10.54% and 9.99% of patients, respectively. Moreover, 20.48% of patients experienced over-reaction to insect bites. Allergic rhinitis, asthma, and allergic conjunctivitis were found in 20.71%, 2.68%, and 2.23% of patients, respectively. A history of atopic diseases in first-, second-, and third-degree relatives was found in 31.29%, 6.81%, and 2.68% of patients, respectively. Advanced age, female, living in urban areas, smoking, atopic comorbidities, and an atopic family history were associated with increased risk of AD [Table 1]. Table 1 - Characteristics, atopic comorbidities, and atopic family history in adult patients with atopic dermatitis and general population. Items Atopic dermatitis (N = 2202) General population (N = 34,498) P values Age (years) 37.09 ± 15.83 35.48 ± 15.64 < 0.001 Gender < 0.001 Male 872 (39.60) 14,981 (43.43) Female 1330 (60.40) 19,517 (56.57) Residence < 0.001 Rural 79 (3.59) 2979 (8.64) Urban 2123 (96.41) 31,519 (91.36) Smoking Current smoker 319 (14.49) 4935 (14.31) 0.004 Ex-smoker 134 (6.08) 1571 (4.55) Nonsmoker 1749 (79.43) 27,992 (81.14) Food allergy 232 (10.54) 1661 (4.81) < 0.001 Drug allergy 220 (9.99) 1891 (5.48) < 0.001 Over-reaction to insect bites 451 (20.48) 3375 (9.78) < 0.001 Allergic rhinitis 456 (20.71) 3249 (9.42) < 0.001 Asthma 59 (2.68) 369 (1.07) < 0.001 Allergic Conjunctivitis 49 (2.23) 302 (0.88) < 0.001 Atopy in first-degree relatives 689 (31.29) 4328 (12.55) < 0.001 Atopy in second-degree relatives 150 (6.81) 920 (2.67) < 0.001 Atopy in third-degree relatives 59 (2.68) 376 (1.09) < 0.001 Data are expressed as mean ± standard deviation or n (%). The logistic regression model including region, age, and sex showed no significant difference in the prevalence of AD among regions [Supplementary Table 1, https://links.lww.com/CM9/B405]. In the multivariate logistic regression model, female, advanced age (≥60 years), living in urban areas, and smoking were risk factors for AD. Other risk factors included food allergy, drug allergy, over-reaction to insect bites, allergic rhinitis, asthma, and atopy in first- and second-degree relatives [Supplementary Table 2, https://links.lww.com/CM9/B405]. Of all patients with AD, 65.67% had visited dermatolo-gists and 18.71% had visited traditional Chinese medicine (TCM) doctors. Self-treatment was found in 40.42% of patients, and 3.59% had left their AD untreated. Topical corticosteroids and calcineurin inhibi-tors were used in 64.85% and 4.50% of patients, respectively. Fewer patients used phototherapy (1.18%). Antihistamines, systemic steroids, and immunosuppressants were used in 35.51%, 2.18%, and 0.73% of patients, respectively. Moreover, 12.53% of patients used oral TCM and 11.81% used topical TCM. In this study, the 1-year prevalence of dermatologist-diagnosed AD in Chinese adults was 6.13%. In previous reports, the 1-year prevalence of physician-diagnosed AD in adults ranged from 1.2% to 17.1%.[2,3] The prevalence by clinical diagnosis is often higher than that by criteria-based diagnosis in these studies. For example, a study showed that the prevalence of childhood AD was 12.94% based on dermatologists’ diagnosis but was only 4.76% using the UK Working Party criteria.[1] In our study, the prevalence of AD was only 1.86% using the UK Working Party criteria. Patients who met the diagnostic criteria usually had typical AD, whereas those who did not often had atypical or mild AD. In this study, 66.08% of patients had adult-onset AD, suggesting that late-onset AD is common. Liu et al[4] also reported that 77.5% of adult and adolescent patients with AD experienced the first onset of disease after 12 years of age. The present study showed that the hands, lower legs, neck, and face were more commonly affected in adult AD, consistent with a previous study.[5] We found that most patients (73.33%) had mild AD, whereas moderate and severe AD were found in 24.78% and 1.89% of patients, respectively, similar to the findings in pediatric patients.[1] This study showed that AD was more in women than in men, consistent with most studies.[2] AD was also more common in urban than rural areas, which might be related to lifestyle. Food allergy, drug allergy, and over-reaction to insect bites were common in patients with AD. Allergic rhinitis, asthma, and allergic conjunctivitis were found in 20.71%, 2.68%, and 2.23% of patients with AD, respectively. An atopic family history was also commonly found in adult patients with AD. In this study, 18.71% of patients with AD went to TCM doctors and 40.42% patients chose self-treatment, suggesting high diversity of treatment options among Chinese adults with AD. A small number of patients (3.59%) chose not to treat their AD. These patients might have had mild AD. Topical corticosteroids (64.85%) were the most common topical treatment. Systemic steroids and immunosuppressants were used in only 2.18% and 0.73% of patients, respectively. Although this was a large-scale, nationwide, population-based survey, it has some limitations. The cross-sectional design restricted the exploration of cause-effect relationship. The sample size and the sex and age distributions were not balanced among provinces. Only a few comorbidities were studied. We hope that these limitations will be overcome in future studies. In conclusion, the 1-year prevalence of AD in Chinese adults was 6.13%. The point prevalence of AD was 2.42%. Female, living in urban areas, smoking, atopic comorbidities, and an atopic family history were associated with increased risk of AD. Acknowledgements Authors thank all investigators for their contributions to this study, and all participants for their substantial support. Funding This study was partly supported by grants from the National Natural Science Foundation of China (No. 81442005 and No. 82103750). Conflicts of interest None.

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