Adult hospitalizations for laboratory-positive influenza during the 2005-2006 through 2007-2008 seasons in the United States.
BACKGROUND
Rates of influenza-associated hospitalizations in the United States have been estimated using modeling techniques with data from pneumonia and influenza hospitalization discharge diagnoses, but they have not been directly estimated from laboratory-positive cases.


METHODS
We calculated overall, age-specific, and site-specific rates of laboratory-positive, influenza-associated hospitalization among adults and compared demographic and clinical characteristics and outcomes of hospitalized cases by season with use of data collected by the Emerging Infections Program Network during the 2005-2006 through 2007-2008 influenza seasons.


RESULTS
Overall rates of adult influenza-associated hospitalization per 100,000 persons were 9.9 during the 2005-2006 season, 4.8 during the 2006-2007 season, and 18.7 during the 2007-2008 season. Rates of hospitalization varied by Emerging Infections Program site and increased with increasing age. Higher overall and age-specific rates of hospitalization were observed during influenza A (H3) predominant seasons and during periods of increased circulation of influenza B. More than 80% of hospitalized persons each season had > or =1 underlying medical condition, including chronic cardiovascular and metabolic diseases.


CONCLUSIONS
Rates varied by season, age, geographic location, and type/subtype of circulating influenza viruses. Influenza-associated hospitalization surveillance is essential for assessing the relative severity of influenza seasons over time and the burden of influenza-associated complications.
Dao
Christine N
CN
Influenza Division, Centers for Disease Control and Prevention, Atlanta, Georgia 30333, USA.
Kamimoto
Laurie
L
Nowell
Mackenzie
M
Reingold
Arthur
A
Gershman
Ken
K
Meek
James
J
Arnold
Kathryn E
KE
Farley
Monica
M
Ryan
Patricia
P
Lynfield
Ruth
R
Morin
Craig
C
Baumbach
Joan
J
Hancock
Emily
E
Zansky
Shelley
S
Bennett
Nancy M
NM
Thomas
Ann
A
Vandermeer
Meredith
M
Kirschke
David L
DL
Schaffner
William
W
Finelli
Lyn
L
D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D005843:Geography; D006760:Hospitalization / Q000706:statistics & numerical data*; D006801:Humans; D007251:Influenza, Human / Q000453:epidemiology* / Q000473:pathology* / Q000821:virology; D008297:Male; D008875:Middle Aged; D009975:Orthomyxoviridae / Q000302:isolation & purification*; D015995:Prevalence; D012307:Risk Factors; D014481:United States / Q000453:epidemiology; D055815:Young Adult