Seasonal variation in the superficial vein thrombosis frequency

ABSTRACTIntroductionA seasonal variation of venous thromboembolic disease frequency is subject to discussion, and has been recently suggested for superficial vein thrombosis (SVT) in a small retrospective study. Our aim was to search for a seasonal variation of SVT frequency according to the data of larger studies.Materials and methodsWe analyzed the data of three French prospective multicenter studies with different designs which have included patients with SVT (STENOX, POST, and STEPH studies). Seasonal variation of SVT frequency was evaluated by comparing the observed seasonal frequency of SVT to a theoretical frequency of 25% for each season.ResultsThe analysis included 1395 patients and 4.75 seasonal cycles. The difference to a theoretical frequency of 25% was statistically significant in one study (POST, p = 0.044). The higher risk difference was − 6.1% (95% CI − 11.7-−0.5) in summer in STENOX, + 7.1% (95% CI + 2.7-+11.5) in winter in POST and 4.2% (95% CI − 5.2-+13.7) in spring in STEPH, corresponding to a relative risk of 0.80, 1.40 and 1.20, respectively.ConclusionsA seasonal variation was found in only one study which has the weakest methodology to warrant completeness. Variation pattern was different in each study. If this variation exists, it would probably be too low to have clinical consequences.