title: Estimating the Burden of Pandemic Infectious Disease: The Case of the Second Wave of Pandemic Influenza H1N1 in Forsyth County, North Carolina.
abstract: BACKGROUND
  Understanding the burden of influenza A(H1N1)pdm09 virus during the second wave of 2009-2010 is important for future pandemic planning.
  
  
  METHODS
  Persons who presented to the emergency department (ED) or were hospitalized with fever and/or acute respiratory symptoms at the academic medical center in Forsyth County, North Carolina were prospectively enrolled and underwent nasal/throat swab testing for influenza A(H1N1)pdm09. Laboratory-confirmed cases of influenza A(H1N1)pdm09 virus identified through active surveillance were compared by capture-recapture analysis to those identified through independent, passive surveillance (physician-ordered influenza testing). This approach estimated the number of total cases, including those not captured by either surveillance method. A second analysis estimated the total number of influenza A(H1N1)pdm09 cases by multiplying weekly influenza percentages determined via active surveillance by weekly counts of influenza-associated discharge diagnoses from administrative data. Market share adjustments were used to estimate influenza A(H1N1)pdm09 virus ED visits or hospitalizations per 1,000 residents.
  
  
  RESULTS
  Capture-recapture analysis estimated that 753 residents (95% confidence interval [CI], 424-2,735) with influenza A(H1N1)pdm09 virus were seen in the academic medical center from September 2009 through mid-April 2010; this result yielded an estimated 4.7 (95% CI, 2.6-16.9) influenza A(H1N1)pdm09 virus ED visits or hospitalizations per 1,000 residents. Similarly, 708 visits were estimated using weekly influenza percentages and influenza-associated discharge diagnoses, yielding an estimated 4.4 influenza A(H1N1)pdm09 virus ED visits or hospitalizations per 1,000 residents.
  
  
  CONCLUSIONS
  This study demonstrates that the burden of influenza A(H1N1)pdm09 virus in ED and inpatient settings by capture-recapture analysis was 4-5 per 1,000 residents; this rate was approximately 8-fold higher than that detected by physician-ordered influenza testing.
authors.affiliation: associate professor, Departments of Pediatrics, Wake Forest School of Medicine, Winston-Salem, North Carolina tpeters@wakehealth.edu.
authors.forename: Timothy R
authors.initials: TR
authors.lastname: Peters
authors.affiliation: professor, Biostatistical Sciences, Wake Forest School of Medicine, Winston-Salem, North Carolina.
authors.forename: Beverly M
authors.initials: BM
authors.lastname: Snively
authors.affiliation: biostatistician, Biostatistical Sciences, Wake Forest School of Medicine, Winston-Salem, North Carolina.
authors.forename: Cynthia K
authors.initials: CK
authors.lastname: Suerken
authors.affiliation: director of infection control and associate professor, Internal Medicine, Wake Forest School of Medicine, Winston-Salem, North Carolina.
authors.forename: Werner
authors.initials: W
authors.lastname: Bischoff
authors.affiliation: research associate, Departments of Pediatrics, Wake Forest School of Medicine, Winston-Salem, North Carolina.
authors.forename: Lauren
authors.initials: L
authors.lastname: Vannoy
authors.affiliation: research associate, Departments of Pediatrics, Wake Forest School of Medicine, Winston-Salem, North Carolina.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Blakeney
authors.affiliation: public health epidemiologist, Internal Medicine, Wake Forest School of Medicine, Winston-Salem, North Carolina.
authors.forename: Tammy
authors.initials: T
authors.lastname: Bischoff
authors.affiliation: associate professor, Pathology, Wake Forest School of Medicine, Winston-Salem, North Carolina.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Palavecino
authors.affiliation: professor, Internal Medicine, Wake Forest School of Medicine, Winston-Salem, North Carolina.
authors.forename: Robert
authors.initials: R
authors.lastname: Sherertz
authors.affiliation: professor, Departments of Pediatrics, Epidemiology and Prevention, Wake Forest School of Medicine, Winston-Salem, North Carolina.
authors.forename: Katherine A
authors.initials: KA
authors.lastname: Poehling
mesh_terms: D000293:Adolescent; D000328:Adult; D002648:Child; D002675:Child, Preschool; D004636:Emergency Service, Hospital / Q000706:statistics & numerical data; D005260:Female; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D053118:Influenza A Virus, H1N1 Subtype; D007251:Influenza, Human / Q000453:epidemiology*; D008297:Male; D008875:Middle Aged; D009657:North Carolina; D058873:Pandemics; D055815:Young Adult