Validation of the U.K. Working Party diagnostic criteria for atopic eczema in a Xhosa-speaking African population

BACKGROUND: Reliable diagnostic criteria for eczema are important for epidemiological comparisons. Although the U.K. diagnostic criteria for atopic eczema have performed well in an English language setting, limited data are available from other countries where cultural and linguistic factors may affect their validity. OBJECTIVES: We sought to determine the validity of the U.K. criteria for eczema in relation to clinical assessment by a dermatologist in a Xhosa-speaking South African population. METHODS: A cross-sectional survey of 3067 children aged 3-11 years was conducted in rural, peri-urban and urban settings in South Africa. The prevalence of atopic eczema was determined using the U.K. diagnostic criteria and a clinical assessment by a dermatologist. Questions were translated into the local language (Xhosa). Trained researchers administered the questions to the children's parents or carers. The validity of the U.K. criteria was then determined by calculating the sensitivity, specificity, positive and negative predictive values, and Youden's Index in relation to the dermatologist's examination. RESULTS: The point prevalence of atopic eczema according to a dermatologist was 1.0% 95% confidence interval (CI) 0.6-1.4], while the prevalence of visible flexural eczema according to the U.K. protocol was 1.8% (95% CI 1.3-2.2). The sensitivity and specificity of the U.K. criteria in this setting was 43.7% (95% CI 26.3-62.3) and 97.9% (97.3-98.4), respectively. The positive and negative predictive values of the U.K. criteria were 18.4% (95% CI 10.4-28.9) and 99.4% (95% CI 99.0-99.6), respectively. The presence of visible flexural eczema according to the U.K. photographic protocol was the best predictor of atopic eczema, with a sensitivity and specificity of 81.2% (95% CI 63.5-92.7) and 99.0% (95% CI 98.6-99.3), respectively, and a positive and negative predictive value of 48.1% (95% CI 34.3-62.1) and 99.8% (95% CI 99.5-99.9), respectively. CONCLUSIONS: The validity of the full question-based version of the U.K. diagnostic criteria for atopic eczema in this South African setting is low, which may be due to a combination of translational and cultural issues. However, the one physical sign of visible flexural eczema performed well, suggesting that it alone might be a useful tool for future international comparative prevalence studies.