Seasonal variation in the occurrence of venous thromboembolism: a report from the Korean Venous Thromboembolism Working Party.

There have been conflicting results on seasonal variation in the occurrence of venous thromboembolism (VTE). It also has never been studied in Asian population. To address these issues, we investigated seasonal changes of the incidence of VTE in Korean population using 1,495 patients with VTE between January 2001 and December 2010. VTE occurred most frequently in the winter and least frequently in the summer (χ2=11.83, P=0.008). In the subset analyses, the same trend was shown in the PE±DVT group, the unprovoked VTE group, and the VTE without malignancy group. The monthly occurrence rate peaked in December and was at its lowest in July (P=0.004). In conclusion, our study provides evidence that there is an increased risk for VTE in Korean population in the winter season.