BACKGROUND: The triggering factors of venous thromboembolic disease have been increasingly clarified. External causes may influence its occurrence, and some climactic factors have stood out. Nothing is known about such interference in our latitude. OBJECTIVES: To determine whether there are seasonal variations in venous thromboembolism in a hospital-based population in São Paulo, Brazil, which has subtropical climate. METHODS: Medical records of patients admitted to Hospital da Beneficência Portuguesa de São Paulo with the diagnosis of deep venous thrombosis or pulmonary thromboembolism were reviewed from January 1996 to October 2003. Cases were grouped in trimesters (first trimester = January, February and March; second trimester = April, May and June; third trimester = July, August and September; fourth trimester = October, November and December). They were also grouped as to warm and cold months, according to mean temperature (warm months = October through April; cold months = May through September). RESULTS: A total of 955 cases of venous thromboembolism were found during the study period. The ANOVA test was used for statistical analysis, showing no significant difference in the occurrence of venous thromboembolism considering the four trimesters. Separate analysis of deep venous thrombosis and pulmonary embolism incidence showed no differences either. Comparing warm and cold months, there was an increased incidence of deep venous thrombosis during warm months (p < 0.05, Mann-Whitney test). CONCLUSION: Venous thromboembolism is not clearly related to climatic variations. The influence of climate and temperature on blood coagulability is poorly understood and needs to be further studied.
Venous thrombosis; pulmonary embolism; epidemiology; climatology
