[Prevalence of symptoms of asthma, allergic rhinitis, conjunctivitis and atopic eczema: ISAAC (International Study of Asthma and Allergies in Childhood) in a population of schoolchildren in Zagreb].

OBJECTIVE: Numerous studies of the population prevalence of asthma, allergic rhinitis, and atopic eczema revealed some international differences. However, the International Study of Asthma and Allergies in Childhood (ISAAC) was the first one using a standardized methodology to evaluate the prevalence of these diseases, and to make comparisons within and between countries. The results showed marked variations in 12-month prevalence of asthma, allergic rhinoconjunctivitis, and atopic eczema symptoms with 20-fold (range 1.6-36.8%), 30-fold (range 1.4-39.7%), and 60-fold (range 0.3-20.5%) differences between the centres with the highest and the lowest prevalence, respectively.

AIM: Our aim was to gain the insight into the prevalence of allergic diseases in Zagreb, Croatia by the methods of internationally standardized protocol, proposed by the ISAAC Steering Committee.

METHODS: Original questionnaires, translated from English into Croatian, consisting of questions about the child's demographic characteristics, core modules on wheezing, rhinitis and eczema, and supplementary modules, were completed by parents of 10-year-old children (4th grade) attending 18 elementary schools in a city of Zagreb. Total of 1047 questionnaires were returned and analysed after the inconsistent responses were eliminated by phone calling.

DISCUSSION: Phase one of the ISAAC study has shown a wide variation in the prevalence of asthma, allergic rhinoconjunctivitis, and atopic eczema symptoms throughout the world, with differing international patterns for the different disorders. Four prevalence ranges have been established for better illustration of the geographic distribution of asthma prevalence: (I) < 5%; (II) 5 to < 10%; (III) 10 to < 20%; (IV) > or = 20%. The highest 12-month prevalences of asthma symptoms were found in developed countries (UK, Australia, New Zealand, Republic of Ireland, and most centres in North, Central, and South America), being in prevalence range IV. The lowest prevalences (range I) were found in several Eastern European countries, Indonesia, Greece, China, Taiwan, Uzbekistan, India, and Ethiopia. According to the results of our study, a continental part of Croatia with a 12-month prevalence of wheezing of 6.02% corresponds to range II. Prevalence of asthma symptoms was greater in males, which is consistent with the results of the younger age group previously analysed. For allergic rhinoconjunctivitis and atopic eczema symptoms grouping of centres with a high prevalences into specific regions was less well defined than for asthma. Centres with the highest prevalences were scattered across the world. In contrast, centres with the lowest prevalences were similar to those for asthma symptoms. Our results of the 12-month prevalence of allergic rhinoconjunctivitis (12.13%), and atopic eczema (7.83%) symptoms were somewhere between the two extremes. As with asthma symptoms, the prevalence of rhinoconjunctivitis symptoms was greater in males. Contrary, the difference in prevalence of atopic eczema symptoms between the sex groups has not been found. The worldwide variations in prevalence of asthma, allergic rhinoconjunctivitis, and atopic eczema symptoms suggest that environmental factors may be critical to the development of these disorders in childhood. Furthermore, different patterns of geographical distribution of particular disorders suggest that major risk factors for them may be different or may involve different latency periods and time trends. Therefore, studies that include objective clinical assessment are required.

CONCLUSION: According to our results, Zagreb is a city with relatively low prevalence of allergic diseases symptoms. Larger sample size of at least 3000 subjects is required to provide sufficient precision for estimates of symptom severity, and to generate adequate number of subjects with particular disorders for further analyses. Therefore, we recently increased our sample size to more than 3000 subjects, and started ISAAC Phase two (clinical examination, measures of bronchial hyperresponsiveness, measures of atopy, measures of environmental exposure to aeroallergens, and genetic analyses) in Zagreb, Croatia.