Objective: To study variations in climate (dry or rainy periods) and health services use for the treatment of asthma in children under five years of age. Methods: An ecological study was conducted and involved analysis of the medical charts of all children under the age of five that were diagnosed with asthma and treated in the Municipal Emergency Room of the city of Cuiabá, located in the state of Mato Grosso, Brazil. In accordance with the geographic location of Cuiabá, two climatic periods were identified: a dry season (from May to October) and a rainy season (from November to April). Results: The percentage of children treated that were diagnosed with asthma was 12.2% (3140/25,802), with no gender-based difference. Children from 3 to 5 years of age were most often affected. The overall asthma hospitalization rate was 1.3% (336/25,802), rising to 10.7% (336/3140) among the asthmatic children treated in the emergency room. In the rainy season, the percentage of outpatients seeking treatment for asthma was higher than in the dry season: 39.1% (1228/3140) versus 60.9% (1912/3140). However, during the dry season, a greater proportion of such patients were hospitalized: 52.3% (176/336) versus 47.7% (160/336). These differences were statistically significant (p < 0.05). Conclusions: The dry season, which was correlated with higher asthma hospitalization rates, seems to be related to more severe cases of asthma in children under five years of age.

Keywords: Asthma/prevention & control; Allergens/adverse effects; Respiratory hypersensitivity; Environmental monitoring;