Worldwide time trends in prevalence of symptoms of rhinoconjunctivitis in children: Global Asthma Network Phase I.

BACKGROUND: The Global Asthma Network (GAN), by using the International Study of Asthma and Allergies in Childhood (ISAAC) methodology, has updated trends in prevalence of symptoms of childhood allergic diseases, including non-infective rhinitis and conjunctivitis ("rhinoconjunctivitis") which is reported here. METHODS: Prevalence and severity of rhinoconjunctivitis were assessed by questionnaire among schoolchildren in GAN Phase I and ISAAC Phases I and III surveys 15-23 years apart. Absolute rates of change in prevalence were estimated for each centre and modelled by multi-level linear regression to compare trends by age group, time period and per-capita national income. RESULTS: 27 GAN centres in 14 countries surveyed 74,361 13-14-year-olds ("adolescents") and 45,434 6-7-year-olds ("children"), with average response proportions of 90% and 79% respectively. Many centres showed highly significant (p<0.001) changes in prevalence of rhinoconjunctivitis in the past year ("current rhinoconjunctivitis"), compared to ISAAC. The direction and magnitude of centre-level trends varied significantly (p<0.001) both within and between countries. Overall, current rhinoconjunctivitis prevalence decreased slightly from ISAAC Phase III to GAN: -1.32% per 10 years, 95%CI [-2.93%, +0.30%] among adolescents; -0.44% [-1.29%, +0.42%] among children. Together, these differed significantly (p<0.001) from the upward trend within ISAAC. Among adolescents, centre-level trends in current rhinoconjunctivitis were highly correlated with those for eczema symptoms (rho=0.72, p