Short-term exposure to PM2.5 and risk of venous thromboembolism. A case-crossover study

Background: Short-term exposure to air pollution increases the risk of cardiovascular mortality and morbidity but little evidence is available on pollution effects on venous thromboembolism (VTE), a common vascular disease. Methods: We conducted a case-crossover analysis of all urgent hospitalizations for deep vein thrombosis (DVT) or pulmonary embolism (PE) among patients >35 years during the period 2006 to 2017 in Rome (Italy). We examined whether 1) short-term exposure to particulate matter with aerodynamic diameter <2.5 μg (PM2.5) increases the risk of hospitalization for DVT or PE, and 2) if the associations are modified by the period of the year (warm and cold seasons), sex, age and comorbidity. Results: We found that short-term exposure to PM2.5 was associated with an increase of PE hospitalization risk of during the warm season (April to September) of 19.6% (95% confidence intervals: 8.3, 31%) per 10 μg/m3, while no statistically significant effects were displayed during the cold season or the whole year or for DVT hospitalizations. The effect of PM2.5 remained significant (%change: 21.3; 95%CI: 5.4, 39.5) after adjustment for nitrogen dioxide (NO2) co-exposure (a marker of traffic sources) and when limiting to primary diagnosis of PE (%change: 19.1; 95%CI: 4.2, 36.1). Age, sex and comorbid conditions did not modify the association. Conclusions: Our results suggested a positive association between short-term exposure to PM2.5 and pulmonary embolism during the warm period of the year while no evidence emerged for deep vein thrombosis.