title: Estimating age-specific influenza-related hospitalization rates during the pandemic (H1N1) 2009 in Davidson Co, TN.
abstract: BACKGROUND
  In April 2009, a pandemic caused by a novel influenza strain, the A(H1N1)pdm09 virus, started. Few age-specific estimates of hospitalizations associated with the first year of circulation of the pandemic virus are available.
  
  
  OBJECTIVE
  To estimate age-specific hospitalization rates associated with laboratory-confirmed A(H1N1)pdm09 virus in Davidson County, TN, from May 2009 to March 2010.
  
  
  METHODS
  Two separate strategies were applied: capture-recapture and surveillance-sampling methods. For the capture-recapture estimates, we linked data collected via two independent prospective population-based surveillance systems: The Influenza Vaccine Effectiveness Network (Flu-VE) tested consenting county patients hospitalized with respiratory symptoms at selected hospitals using real-time reverse transcriptase polymerase chain reaction (rRT-PCR); the Emerging Infections Program identified county patients with positive influenza tests in all area hospitals. For the surveillance-sampling estimates, we applied the age-specific proportions of influenza-positive patients (from Flu-VE) to the number of acute respiratory illness hospitalizations obtained from the Tennessee Hospital Discharge Data system.
  
  
  RESULTS
  With capture-recapture, we estimated 0·89 (95% CI, 0·72-1·49), 0·62 (0·42-1·11), 1·78 (0·99-3·63), and 0·76 (0·50-1·76) hospitalizations per 1000 residents aged < 5, 5-17, 18-49, and ≥ 50 years, respectively. Surveillance-sampling estimated rates were 0·78 (0·46-1·22), 0·32 (0·14-0·69), 0·99 (0·64-1·52), and 1·43 (0·80-2·48) hospitalizations per 1000 residents aged <5, 5-17, 18-49, and ≥ 50 years, respectively. In all age-groups combined, we estimated approximately 1 influenza-related hospitalization per 1000 residents.
  
  
  CONCLUSIONS
  Two independent methods provided consistent results on the burden of pandemic virus in Davidson County and suggested that the overall incidence of A(H1N1)pdm09-associated hospitalization was 1 per 1000 county residents.
authors.affiliation: Department of Preventive Medicine, Vanderbilt University School of Medicine, Nashville, TN 37212, USA.
authors.forename: Astride
authors.initials: A
authors.lastname: Jules
authors.forename: Carlos G
authors.initials: CG
authors.lastname: Grijalva
authors.forename: Yuwei
authors.initials: Y
authors.lastname: Zhu
authors.forename: Keipp H
authors.initials: KH
authors.lastname: Talbot
authors.forename: John V
authors.initials: JV
authors.lastname: Williams
authors.forename: William D
authors.initials: WD
authors.lastname: Dupont
authors.forename: Kathryn M
authors.initials: KM
authors.lastname: Edwards
authors.forename: William
authors.initials: W
authors.lastname: Schaffner
authors.forename: David K
authors.initials: DK
authors.lastname: Shay
authors.forename: Marie R
authors.initials: MR
authors.lastname: Griffin
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D002648:Child; D002675:Child, Preschool; D005260:Female; D006760:Hospitalization / Q000706:statistics & numerical data*; D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype / Q000235:genetics / Q000302:isolation & purification*; D007252:Influenza Vaccines / Q000008:administration & dosage; D007251:Influenza, Human / Q000453:epidemiology* / Q000517:prevention & control / Q000628:therapy* / Q000821:virology; D008297:Male; D008875:Middle Aged; D058873:Pandemics; D011446:Prospective Studies; D013714:Tennessee / Q000453:epidemiology; D055815:Young Adult
chemical_list: D007252:Influenza Vaccines