Methodological considerations for childhood surveillance systems: the case of obesity

An international consensus on the methodology of a public health surveillance system will be essential in order to have a correct understanding of the progress of the growing challenge posed by the epidemic of obesity, to make inter-country comparisons possible, and overall to evaluate the effectiveness of preventive programmes and interventions. Recently, the European Charter on Counteracting Obesity, adopted at the WHO European Ministerial Conference on Counteracting Obesity in November 2006, called as well for the development of internationally comparable core indicators for inclusion in national health surveillance systems to be used for advocacy, policy making and monitoring purposes. At present, however, there is not yet a universal agreement on the appropriate methodology to carry out an epidemiological study or surveillance system to assess the prevalence and incidence of both overweight and obesity and monitor their trends over time in children and adolescents. The current disagreement involves the diagnosis method for overweight and obesity, the reference values and cut-off points to be applied and the age of the subjects. At the moment body mass index (BMI) is the most accepted anthropometric measure to assess overweight and obesity in epidemiological studies. The new WHO child growth standards from 0 to 5 years and the International Obesity Task Force internationally based criteria for overweight and obesity among children and adolescents aged 2 to 18 years are useful tools for international comparisons.