role of viruses and atypical bacteria in asthma exacerbations among children in oporto (portugal). | upper respiratory tract infections are known to be a significant precipitant of acute asthma exacerbations. the aim of this study was to evaluate seasonal trends and the role of these pathogens in asthma exacerbations in school-aged children from oporto (portugal). | 2007 | 17338895 |