title: Hot summers and heart failure: seasonal variations in morbidity and mortality in Australian heart failure patients (1994-2005).
abstract: BACKGROUND
  There are minimal reports of seasonal variations in chronic heart failure (CHF)-related morbidity and mortality beyond the northern hemisphere.
  
  
  OBJECTIVE
  We examined potential seasonal variations with respect to morbidity and all-cause mortality over more than a decade in a cohort of 2961 patients with CHF from a tertiary referral hospital in South Australia subject to mild winters and hot summers.
  
  
  RESULTS
  Seasonal variation across all event-types was observed. CHF-related morbidity peaked in winter (July) and was lowest in summer (February): 70 (95% CI: 65 to 76) vs. 33 (95% CI: 30 to 37) admissions/1000 at risk (p<0.005). All-cause admissions (113 (95% CI: 107 to 120) vs. 73 (95% CI 68 to 79) admissions/1000 at risk, p<0.001) and concurrent respiratory disease (21% vs. 12%, p<0.001) were consistently higher in winter. 2010 patients died, mortality was highest in August relative to February: 23 (95% CI: 20 to 27) vs. 12 (95% CI: 10 to 15) deaths per 1000 at risk, p<0.001. Those aged 75 years or older were most at risk of seasonal variations in morbidity and mortality.
  
  
  CONCLUSIONS
  Seasonal variations in CHF-related morbidity and mortality occur in the hot climate of South Australia, suggesting that relative (rather than absolute) changes in temperature drive this global phenomenon.
authors.affiliation: School of Medicine, University of Queensland, Brisbane, Australia.
authors.forename: Sally C
authors.initials: SC
authors.lastname: Inglis
authors.forename: Robyn A
authors.initials: RA
authors.lastname: Clark
authors.forename: Sepehr
authors.initials: S
authors.lastname: Shakib
authors.forename: Denis T
authors.initials: DT
authors.lastname: Wong
authors.forename: Payman
authors.initials: P
authors.lastname: Molaee
authors.forename: David
authors.initials: D
authors.lastname: Wilkinson
authors.forename: Simon
authors.initials: S
authors.lastname: Stewart
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D015331:Cohort Studies; D005260:Female; D006333:Heart Failure / Q000150:complications* / Q000401:mortality*; D006760:Hospitalization / Q000706:statistics & numerical data; D006358:Hot Temperature; D006801:Humans; D015994:Incidence; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies; D012307:Risk Factors; D012621:Seasons; D012959:Socioeconomic Factors; D013021:South Australia / Q000453:epidemiology