Studies of the prevalence of asthma and allergy i Costa Rican school children

Abstract

Objectives The main aims of our study were: To determine the prevalence and severity of asthma, rhinitis, rhinoconjuntivitis and dermatitis in school children from Costa Rica (I, IV, V) to make international comparisons and to identify possible risk factors associated with these conditions (II, III).Methods Using nationally representative samples of 9931 school children from Costa Rica during the last 10 years (from 1989 to 1998) we have performed three studies. Diagnostic criteria for asthma in study I (1989): using the diagnosis by a doctor in combination with the presence of four kinds of respiratory symptoms; in study II (1995) and III (1998): history of wheeze in the past 12 months. The two latter studies were part of the International Study of Asthma and Allergies in Childhood (ISAAC). In study II, the diagnosis of rhinitis required a history of sneezing, or a runny, or blocked nose without a cold in the last 12 months; if accompanied with itchy-watery eyes, they were considered to have rhinoconjuntivitis. An itchy skin rash in the last 12 months was regarded as atopic eczema. Results: Prevalence of asthma and respiratory symptoms A very high prevalence of a history of wheezing (46.8%, 42.9%, and 45.1 %) and a diagnosis of asthma was found in the three studies (IV). (23.4%, 27.7%, and 27.1 %). The younger group of 6-7 years of age had more often respiratory symptoms than the 13-14 year old group (p<0.001).Prevalence of rhinitis, rhinoconjuntivitis and dermatitis In study II, the prevalence of rhinitis in the last 12 months was 26.6% and rhinoconjuntivitis was 12.1% for the 6-7 year old group. In the 13-14 year old group the presence of rhinitis in the last 12 months was 30.9% and rhinoconjuntivitis was 14.8, showing significantly higher figures for the older group (p=0.0001, p=0.001). The prevalence of "ever having had a diagnosis of rhinitis" was 5.9% and 4.8% in the two age groups (NS).The presence of rash ever was found in 27.2% and 26.3% (NS) in the two age groups. Rash in the past year was 18.4% (6-7 years) and 16.5% (13-14 years) (p=0.04, OR 1.14), while 8.2% and 4.5%, respectively, had had a doctor's diagnosis of eczema (p<0.001, OR 1.87). Analyses of specific IgE antibodies and total serum IgE. The most prevalent IgE antibodies were to mite (Dermatophagoides farinae), cockroach, dog and housedust allergens using MAST pipettes for the measurements. Increased IgE reactivity to housedust, mite (D. farinae), cat and the two molds (Alternaria and Cladosporium) allergens was also significantly more prevalent among the asthmatics than the non asthmatics. The result of the analysis of IgE antibodies to a pool of ten common allergens (Phadiatop) showed allergen sensitization in 57.7 % of the asthmatic children and 42.3 % in the non asthmatic group. The concentration of serum IgE was significantly higher among the asthmatic children, 358 kU/l, than among the non asthmatic children, 248.4 KU/l(p <0.001).Dust analyses Very high levels of guanine, and mite allergens were found particularly in bed dust. Bed and bedroom floor dust contain more guanine and mite allergen in humid than in drier places. More guanine was present in bedroom floor dust in rural than in urban areas (p < 0.001). The number of mites in bed and floor dust was significantly higher in urban than rural (p < 0.001) and temperate areas (p < 0.01), compared to the coastal regions. The bedrooms in the homes in temperate metropolitan area was rich in guanine, Der.p 1, as well as Bla.g 2 were found mainly at the coastal regions. Parallel studies suggest very large numbers of mites in rubber foam mattresses.Conclusion Costa Rica is located in the tropics with a very high humidity, an enormous variety of flora and fauna and a very high prevalence of mite and cockroach allergens, which provide important risk factors that may explain the high prevalence of asthma, asthma-related symptoms, rhinitis and eczema. Further possible factors, such as the increased environmental pollution and changes towards a more western life style, include fewer infections and parasitic diseases in the first years. Especially the very extensive exposure to mites and cockroaches in bed material and in homes with poor ventilation may be an important factor, but many wheezing children behave as non-atopic with a viral respiratory infection as a major precipitating factor.