title: Seasonal variation in the occurrence of deep vein thrombosis.
abstract: BACKGROUND
  The occurrence of several adverse cardiovascular events, eg, myocardial infarction and stroke, is not randomly distributed over time, but shows definite seasonal patterns. The temporal pattern for pulmonary embolism (PE) is known, whereas the data concerning deep vein thrombosis (DVT) are not conclusive. The aim of our study was to investigate whether a seasonal variation exists also for DVT, together with the possible influence of different comorbid risk factors.
  
  
  METHODS
  We observed 1164 consecutive cases of DVT at the General Hospital of Ferrara, Italy, from 1998 to 2002. The total sample was divided into subgroups by gender, and by the most common comorbid conditions. For statistical analysis, the distribution of symptom onset was tested for uniformity by the chi 2 test for goodness of fit, and partial Fourier series were used to assess rhythmicity.
  
  
  RESULTS
  Seasonal analysis showed a significantly reduced frequency of DVT events in summer and increased in winter, for the total population (p<0.0001), men (p=0.003), women (p=0.007), subjects with PE (p=0.001), and hypertension (p=0.001). Similarly, chronobiological analysis yielded a significant seasonal variation, with a peak in December for the total population (p<0.001), men and women (p<0.001 and p=0.02, respectively), PE (p=0.006), and hypertension (p=0.028).
  
  
  CONCLUSIONS
  This study shows the existence of a highly significant seasonal pattern in the occurrence of DVT, characterized by a winter peak. Thus, colder months and relative hypercoagulability could be considered a supplementary high risk condition when prescribing an anticoagulant regimen.
authors.affiliation: Section of Internal Medicine, Gerontology and Geriatrics, Department of Clinical and Experimental Medicine, University of Ferrara, Italy.
authors.forename: Massimo
authors.initials: M
authors.lastname: Gallerani
authors.forename: Benedetta
authors.initials: B
authors.lastname: Boari
authors.forename: Damiana
authors.initials: D
authors.lastname: de Toma
authors.forename: Raffaella
authors.initials: R
authors.lastname: Salmi
authors.forename: Roberto
authors.initials: R
authors.lastname: Manfredini
mesh_terms: D000368:Aged; D000925:Anticoagulants / Q000494:pharmacology / Q000627:therapeutic use; D002909:Chronobiology Phenomena; D005260:Female; D006801:Humans; D006973:Hypertension; D008297:Male; D008875:Middle Aged; D012307:Risk Factors; D012621:Seasons; D012737:Sex Factors; D013997:Time Factors; D020246:Venous Thrombosis / Q000175:diagnosis* / Q000453:epidemiology
chemical_list: D000925:Anticoagulants