ENVIRONMENTAL-FACTORS AND RESPIRATORY HYPERSENSITIVITY - THE AMERICA

Diverse environmental exposure profiles exist in the Americas because of widely different climates, ambient pollutants, and bioaerosols in t hese continents. This paper reviews selected studies from the Americas that support the broad hypothesis that environmental factors contribu te to respiratory hypersensitivity. Processes influenced by environmen tal factors include primary immunologic sensitization, the development and exacerbation of specific immunologic diseases and the activation of nonspecific mechanisms with tissue inflammation, injury and remodel ing. Endpoints resulting from these processes include respiratory symp toms, diseases such as asthma, with measures of disease severity inclu ding medication use and hospitalization rates, and death due to cardio respiratory disease. Studies associate sensitization rates to specific allergens with environmental factors such as humidity and indices of allergen exposure. Regional variation occurs with exposure to outdoor source pollutants such as ozone, but varies by household to bioaerosol s such as dust mite, cat or cockroach allergen. Indoor allergens are a ssociated with asthma while outdoor allergens are associated with alle rgic rhinitis. In a national survey, the atopic sensitization rate in the USA increased with urban residence (defined as towns of population > 2500) and varied by region. Controlled human challenge studies show that ozone increases the response of allergic subjects to allergen. I ncreased ambient photochemical pollution concentrations, of which ozon e is an important component, are associated with increased emergency r oom visits for asthma in cities such as Toronto, New York, Atlanta, an d Mexico City. In Sao Paolo, Brazil, mortality due to childhood respir atory disease was influenced by the ambient levels of NO2. Epidemiolog ic studies including the recent meta-analysis of a large, longitudinal study population associate ambient concentrations of particulate matt er < 10 mu m and respiratory symptoms, disease severity and increased cardiorespiratory deaths. Toxicology studies show that individual vari ation in responsiveness is important in nonspecific inflammatory respo nses to irritant pollutants such as ozone and environmental tobacco sm oke. These studies indicate that environmental factors influence prima ry allergen sensitization, secondary allergic responses, the activatio n of nonspecific inflammatory responses, and the severity of respirato ry diseases, including asthma.