title: Impact of the 2009 influenza pandemic on pneumococcal pneumonia hospitalizations in the United States.
abstract: BACKGROUND
  Infection with influenza virus increases the risk for developing pneumococcal disease. The A/H1N1 influenza pandemic in autumn 2009 provided a unique opportunity to evaluate this relationship.
  
  
  METHODS
  Using weekly age-, state-, and cause-specific hospitalizations from the US State Inpatient Databases of the Healthcare Cost and Utilization Project 2003-2009, we quantified the increase in pneumococcal pneumonia hospitalization rates above a seasonal baseline during the pandemic period.
  
  
  RESULTS
  We found a significant increase in pneumococcal hospitalizations from late August to mid-December 2009, which corresponded to the timing of highest pandemic influenza activity. Individuals aged 5-19 years, who have a low baseline level of pneumococcal disease, experienced the largest relative increase in pneumococcal hospitalizations (ratio, 1.6 [95% confidence interval {CI}, 1.4-1.7]), whereas the largest absolute increase was observed among individuals aged 40-64 years. In contrast, there was no excess disease in the elderly. Geographical variation in the timing of excess pneumococcal hospitalizations matched geographical patterns for the fall pandemic influenza wave.
  
  
  CONCLUSIONS
  The 2009 influenza pandemic had a significant impact on the rate of pneumococcal pneumonia hospitalizations, with the magnitude of this effect varying between age groups and states, mirroring observed variations in influenza activity.
authors.affiliation: Division of International Epidemiology and Population Studies, Fogarty International Center, National Institutes of Health, Bethesda, Maryland 20892, USA. weinbergerdm@mail.nih.gov
authors.forename: Daniel M
authors.initials: DM
authors.lastname: Weinberger
authors.forename: Lone
authors.initials: L
authors.lastname: Simonsen
authors.forename: Richard
authors.initials: R
authors.lastname: Jordan
authors.forename: Claudia
authors.initials: C
authors.lastname: Steiner
authors.forename: Mark
authors.initials: M
authors.lastname: Miller
authors.forename: Cécile
authors.initials: C
authors.lastname: Viboud
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D002675:Child, Preschool; D005260:Female; D006760:Hospitalization / Q000706:statistics & numerical data*; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D053118:Influenza A Virus, H1N1 Subtype / Q000302:isolation & purification / Q000472:pathogenicity*; D007251:Influenza, Human / Q000150:complications* / Q000821:virology; D008297:Male; D008875:Middle Aged; D058873:Pandemics; D011018:Pneumonia, Pneumococcal / Q000453:epidemiology*; D014481:United States / Q000453:epidemiology; D055815:Young Adult