[Time trends in the prevalence of asthma and allergic diseases over 7 years among adolescents in Guangzhou city].

OBJECTIVE: To assess time trends in the prevalence of asthma, allergic rhinitis and eczema in Guangzhou urban adolescents.

METHODS: A cross-sectional study using the International Study of Asthma and Allergies in Childhood (ISAAC) Phase III protocol was conducted in 2001. Cluster randomized samples of 3516 schoolchildren aged 13 - 14 from 10 secondary schools of four central districts were recruited for the study in Guangzhou city. The results were compared with those obtained in ISAAC Phase I Study (1994 - 1995), which used the identical and validated core questionnaires. Each subject was given an ISAAC Phase III written questionnaire to complete, followed by the video questionnaire about asthma at the same session in school.

RESULTS: The prevalence rate of physicians' diagnosis of asthma in Phase III was 4.6%, which was similar to that of 3.9% in Phase I (P > 0.05). But the prevalence rates of wheeze and exercise-induced wheeze in the past 12 months by written questionnaire have increased from 3.4% and 17.4% in Phase I to 4.8% and 23.4% in Phase III respectively (all P < 0.01). By the video questionnaire, the 12-months prevalence rates of wheeze at rest and exercise-induced wheeze were also significantly higher in Phase III (3.8% and 11.3%) compared with those in Phase I (2.0% and 6.9%) (P < 0.01). The 12-months prevalence rates of nasal symptoms without common cold, both related to rhinitis and rhinoconjunctivitis had also increased from 39.5% and 8.7% in Phase I to 45.5% and 11.1% in Phase III, respectively (both P < 0.01). Meanwhile, the prevalence rates of physicians' diagnosis of hayfever and allergic rhinitis in Phase III were 4.1% and 22.7%, which were significantly higher than that of 2.9% and 17.4% in Phase I (both P < 0.05). The 12-months prevalence rate of flexural eczema symptoms had increased from 1.3% in Phase I to 2.2% in Phase III (P < 0.01). However, the prevalence rates of physicians' diagnosis of eczema were similar in both surveys (P > 0.05). The absolute percentage changes in 12-months prevalence rate related to symptoms and physicians' diagnosis for asthma, allergic rhinitis and eczema were more in males than those in females.

CONCLUSION: There is a general tendency towards an increase in the prevalence of asthma, allergic rhinitis and eczema over 7 years among adolescents in Guangzhou city, remarkably more so among males than females.