title: Influenza circulation and the burden of invasive pneumococcal pneumonia during a non-pandemic period in the United States.
abstract: BACKGROUND
  Animal models and data from influenza pandemics suggest that influenza infection predisposes individuals to pneumococcal pneumonia. Influenza may contribute to high winter rates of pneumococcal pneumonia during non-pandemic periods, but the magnitude of this effect is unknown. With use of United States surveillance data during 1995-2006, we estimated the association between influenza circulation and invasive pneumococcal pneumonia rates.
  
  
  METHODS
  Weekly invasive pneumococcal pneumonia incidence, defined by isolation of pneumococci from normally sterile sites in persons with clinical or radiographic pneumonia, was estimated from active population-based surveillance in 3 regions of the United States. We used influenza virus data collected by World Health Organization collaborating laboratories in the same 3 regions in seasonally adjusted negative binomial regression models to estimate the influenza-associated fraction of pneumococcal pneumonia.
  
  
  RESULTS
  During approximately 185 million person-years of surveillance, we observed 21,239 episodes of invasive pneumococcal pneumonia; 485,691 specimens were tested for influenza. Influenza circulation was associated with 11%-14% of pneumococcal pneumonia during periods of influenza circulation and 5%-6% overall. In 2 of 3 regions, the association was strongest when influenza circulation data were lagged by 1 week.
  
  
  CONCLUSIONS
  During recent seasonal influenza epidemics in the United States, a modest but potentially preventable fraction of invasive pneumococcal pneumonia was associated with influenza circulation.
authors.affiliation: Epidemic Intelligence Service, Office of Workforce and Career Development Centers for Disease Control and Prevention, Atlanta, Georgia, USA. Nicholas.Walter@ucdenver.edu
authors.forename: Nicholas D
authors.initials: ND
authors.lastname: Walter
authors.forename: Thomas H
authors.initials: TH
authors.lastname: Taylor
authors.forename: David K
authors.initials: DK
authors.lastname: Shay
authors.forename: William W
authors.initials: WW
authors.lastname: Thompson
authors.forename: Lynnette
authors.initials: L
authors.lastname: Brammer
authors.forename: Scott F
authors.initials: SF
authors.lastname: Dowell
authors.forename: Matthew R
authors.initials: MR
authors.lastname: Moore
mesh_terms: D000293:Adolescent; D000328:Adult; D002648:Child; D002675:Child, Preschool; D006801:Humans; D008875:Middle Aged; D009975:Orthomyxoviridae / Q000502:physiology*; D011018:Pneumonia, Pneumococcal / Q000453:epidemiology* / Q000821:virology*; D014481:United States; D055815:Young Adult