title: Seasonal variation in heart failure hospitalization.
abstract: BACKGROUND
  A seasonal variation has been reported for occurrence of acute cardiovascular events, such as myocardial infarction, sudden death, and rupture/dissection of aortic aneurysms.
  
  
  OBJECTIVE
  The aim of this study was to determine whether a seasonal variation exists for heart failure (HF) hospitalization.
  
  
  METHODS
  The study included all cases of HF admissions to Ferrara Hospital between January 2002 and December 2009. The sample was divided into subgroups by gender, age, cardiovascular risk factors, patients' outcome, and order of ICD-9 codes (first diagnosis, accessory diagnosis). On the basis of date of admission, cases have been analyzed for seasonal variation and annual frequency. For seasonal analysis, monthly cases were categorized into four 3-month intervals by seasons. Moreover, monthly admissions have been also adjusted for number of days, and the average number of admissions per month has been used.
  
  
  RESULTS
  The database included 15,954 patients with the ICD-9-CM codes of HF (420-429). Hospital admissions for HF were most frequent in winter (28.4%) and least in summer (20.4%). Chronobiological analysis yielded a significant peak in January for total cases and all subgroups considered. No differences were found for subgroups by gender, age, fatal cases, presence of hypertension and diabetes mellitus, patients' outcome, and order of ICD-9 codes (first diagnosis, accessory diagnosis).
  
  
  CONCLUSIONS
  A seasonal periodicity for HF hospitalization was demonstrated, with a peak in winter months, independent of gender, age, major cardiovascular risk factor, and patients' outcome. These data could be useful for practitioners to improve causative prevention measures, therapeutic management, and educational strategies.
authors.affiliation: Department of Internal Medicine, Hospital of Ferrara, Italy. m.gallerani@ospfe.it
authors.forename: Massimo
authors.initials: M
authors.lastname: Gallerani
authors.forename: Benedetta
authors.initials: B
authors.lastname: Boari
authors.forename: Fabio
authors.initials: F
authors.lastname: Manfredini
authors.forename: Roberto
authors.initials: R
authors.lastname: Manfredini
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D016009:Chi-Square Distribution; D005260:Female; D006333:Heart Failure / Q000453:epidemiology*; D006760:Hospitalization / Q000706:statistics & numerical data*; D006801:Humans; D007558:Italy / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies; D018570:Risk Assessment; D012307:Risk Factors; D012621:Seasons