Short-term effects of air pollution on hospital admissions of respiratory diseases in Hamadan, Iran, 2015 to 2021.

The short-term effects of air pollution on respiratory diseases have been reported in many countries. Urban areas are most affected because of the many sources of pollution and the large number of people living there. This study aims to investigate the effect of short-term exposure to air pollutants on respiratory hospital admissions in the city of Hamadan. In this ecological study, daily hospital admission data were collected from Shahid Beheshti Hospital in Hamadan. Daily information on air pollutants (CO, SO 2 , NO 2 , O 3 , PM 2.5 and PM 10 ) from Hamadan Department of Environment (DoE) organization and of climate factors from Hamadan Meteorological Office were collected. A negative binomial regression model was used to examine the effect of air pollution on daily respiratory hospitalizations. The effect of exposure to pollutants was measured whit different time lags (0-7 days). Furthermore, the effect of meteorological variables was controlled. Subgroup analyses were performed by sex and age group. A total of 12,454 hospitalizations for respiratory diseases were recorded. Results showed a strong and immediate effect of CO on respiratory hospital admissions with highest association at lag 7 (relative risk (RR) = 1.38, 95% CI: 1.33, 1.42). The effects of CO and SO 2 on respiratory hospitalizations are greater for men than women. Regarding the short-term effects of PM 2.5 , SO 2 and O 3 , adults (aged less than 65) were more prone to hospitalization for respiratory diseases. These results show that exposure to air pollution, particularly CO, may increase hospital admissions due to respiratory illness. So reducing the concentration of these pollutants can reduce the number of hospital admissions.