Despite current regulations, which limit the levels of certain
air pollutants, there are still a number of adverse health effects that result from exposure to these agents. Numerous epidemiological studies have noted an association between the levels of air pollution and hospital admissions for a variety of different health reasons, including a number of
respiratory diseases, as well as increased morbidity and mortality associated with various respiratory conditions and diseases. Because of the large impact respiratory
virus infections have on morbidity and even mortality, it is important to understand whether and how exposure to common
air pollutants could exacerbate the susceptibility to and severity of respiratory
virus infections. This review focuses on current epidemiological and experimental studies, which have examined the association between and effect of
air pollutants and respiratory
viral infections, as well as potential mechanisms associated with these effects. Examined in this review are U.S. Environmental Protection Agency (EPA) "criteria"
pollutants nitrogen dioxide (NO(2)),
ozone (O(3)), and
particulate matter (PM), as well as indoor
pollutants such as environmental tobacco
smoke (ETS) and combustion products of biomass fuels. Although a number of studies indicate associations between exposure to
air pollutants and increased risk for respiratory
virus infections, potential mechanisms mediating these effects are largely unexplored. Therefore, additional studies, both epidemiologic and mechanistic, are necessary to increase our understanding of how exposure to
air pollutants could affect respiratory
virus infections, especially in populations already at risk of developing significant morbidity/mortality after
infections with respiratory viruses.