title: Seasonal variation: mortality from pulmonary fibrosis is greatest in the winter.
abstract: BACKGROUND
  In the general population, rates of certain respiratory infections (and mortality from these infections) are higher in winter. We hypothesized that in patients with idiopathic pulmonary fibrosis (IPF) and/or pulmonary fibrosis (PF) from any cause, death rates would be increased during the winter season, independent of recognized infection. Our objective was to determine if mortality rates from IPF and/or PF of any cause exhibit seasonal variation.
  
  
  METHODS
  Using death records from the National Center for Health Statistics, we calculated monthly mortality rates for persons with PF and developed a multivariable model to determine if these mortality rates exhibited seasonal variation.
  
  
  RESULTS
  From spring of 1992 to fall of 2003, there were 27,367,580 deaths in the United States and 170,984 decedents with PF. The average mortality rate among all persons with PF was 17.1% higher in winter (p < 0.0001), 12.7% higher in spring (p < 0.0001), and 5.2% higher in fall (p = 0.0002) than in summer months. These findings persisted when records with a diagnostic code for pneumonia were excluded from the analysis as well as when only records in which PF was the underlying cause of death were included in the analysis.
  
  
  CONCLUSIONS
  Mortality rates from PF exhibit significant seasonal variation, with the highest rates occurring in the winter, even when recognized infection is excluded. Further studies are necessary to determine if this seasonal variation exists in a prospective cohort and, if so, to uncover its etiology.
authors.affiliation: Division of Pulmonary Sciences and Critical Care Medicine, University of Colorado Health Sciences Center, Denver, CO. Electronic address: amy.olson@uchsc.edu.
authors.forename: Amy L
authors.initials: AL
authors.lastname: Olson
authors.affiliation: Interstitial Lung Disease Division, National Jewish Medical and Research Center, Denver, CO.
authors.forename: Jeffrey J
authors.initials: JJ
authors.lastname: Swigris
authors.affiliation: Division of Pulmonary and Critical Care Medicine, University of Washington Medical Center, Seattle, WA.
authors.forename: Ganesh
authors.initials: G
authors.lastname: Raghu
authors.affiliation: Interstitial Lung Disease Division, National Jewish Medical and Research Center, Denver, CO.
authors.forename: Kevin K
authors.initials: KK
authors.lastname: Brown
mesh_terms: D006801:Humans; D009309:National Center for Health Statistics, U.S.; D011014:Pneumonia / Q000150:complications / Q000401:mortality; D016012:Poisson Distribution; D015995:Prevalence; D011658:Pulmonary Fibrosis / Q000150:complications / Q000401:mortality* / Q000473:pathology; D012044:Regression Analysis; D012189:Retrospective Studies; D012621:Seasons; D015996:Survival Rate; D014481:United States / Q000453:epidemiology