Analysis of occurrence of venous thromboembolic disease in the four seasons.

Reports of seasonal variation of the incidence of pulmonary embolism and deep venous thrombosis are inconsistent as to when or if it occurs. We used data from the National Hospital Discharge Survey and the United States (US) Bureau of the Census to test for circannual variation throughout the entire US and in regions of the US over a period of 21 years. Pulmonary embolism, deep venous thrombosis, or the combination did not show seasonal variation in the US or in any region of the US, including the Southern region, where winters are mild, and the northeastern and midwestern regions, where seasons are sharply defined.