Seasonal variability and meteorological factors: retrospective study of the incidence of pulmonary embolism from a large United kingdom teaching hospital.

BACKGROUND Seasonal variations in the incidence of pulmonary embolism (PE) have been reported. It has been suggested that changes in meteorological factors may explain this variation. Previous studies have provided inconsistent results, possibly as a result of a small number of observations, in some studies and confounding factors. OBJECTIVE To investigate whether there is a seasonal variation in the incidence of idiopathic PE and to investigate its relationship with atmospheric pressure, humidity, and temperature. METHODS A large retrospective study was conducted. All confirmed cases of PE at our institution over a 9-year period were included, except for those patients with a major risk factor for PE. Meteorological data were obtained from a local weather station. Days when there was at least one episode of PE (event day) were compared with days when there were no episodes of PE (non-event day). RESULTS There were a total of 640 episodes of PE. There was a statistically significant lower percentage of event days in spring (13.8%), compared with the rest of the year (18.3%) (P = .003). The incidence of PE was related to decreased atmospheric pressure and increased temperature. For atmospheric pressure the relationship was most significant for the mean atmospheric pressure for the 2 days preceding clinical presentation with PE (P = .02). For temperature the relationship was most significant for the mean temperature for the 5 days preceding clinical presentation with PE (P = .04). CONCLUSIONS The results confirm the presence of seasonal variations in episodes of idiopathic PE and an association between decreased atmospheric pressure and increased temperature.