Short-term effects of air pollutants on hospitalization rate in patients with cardiovascular disease: a case-crossover study

Considering the increasing rate of hospitalization due to the symptoms intensification, and the increasing trend of air pollution, this study aimed to determine the relationship between the amount of air pollutants and the incidence of cardiovascular disease leading to hospitalization. This case-crossover study was carried out on the data of admitted patients with cardiovascular disease such as hypertension, ischemic heart disease, and cerebrovascular disease in Urmia during 2011–2016. Weather data about air pollutants (NO2, PM10, SO2, and CO) were obtained from the meteorological department of Urmia. The data were coded for each patient and matched with the meteorological data for statistical modeling. The data were analyzed through STATA version 14. Conditional logistic regression was used to estimate the effects of air pollutants on cardiovascular disease adjusted to air temperature, relative humidity, and air pollutants. The final analysis was performed on 43,424 patients with cardiovascular disease using code I10-I99 including ischemic heart disease, hypertension, and cerebrovascular disease adjusted to air temperature and relative humidity. Of all pollutants, CO with each increase 10 μg/m³ had a meaningful relationship with the incidence of cardiovascular hospitalization. By selecting the window of exposure, 1, 2, and 6 days before admission, lag 6 (6 days) was the best estimation for exposure time in the patients with cardiovascular patients (OR 1.0056, CI 1.0041–1.007), and in the patients with ischemic heart disease (OR 1.000055, CI 1.000036–1.000075) and in the patients with hypertension (OR 1.000076, CI 1.00002–1.000132). Regarding cerebrovascular disease, no statistically significant association was observed. The results showed that only CO was associated with an increased risk of admission in patients with cardiovascular disease, ischemic heart disease, and hypertension, and there was no clear evidence for pollution effects on cerebrovascular diseases.