Outbreak of variant influenza A(H3N2) virus in the United States.
BACKGROUND
Variant influenza virus infections are rare but may have pandemic potential if person-to-person transmission is efficient. We describe the epidemiology of a multistate outbreak of an influenza A(H3N2) variant virus (H3N2v) first identified in 2011.


METHODS
We identified laboratory-confirmed cases of H3N2v and used a standard case report form to characterize illness and exposures. We considered illness to result from person-to-person H3N2v transmission if swine contact was not identified within 4 days prior to illness onset.


RESULTS
From 9 July to 7 September 2012, we identified 306 cases of H3N2v in 10 states. The median age of all patients was 7 years. Commonly reported signs and symptoms included fever (98%), cough (85%), and fatigue (83%). Sixteen patients (5.2%) were hospitalized, and 1 fatal case was identified. The majority of those infected reported agricultural fair attendance (93%) and/or contact with swine (95%) prior to illness. We identified 15 cases of possible person-to-person transmission of H3N2v. Viruses recovered from patients were 93%-100% identical and similar to viruses recovered from previous cases of H3N2v. All H3N2v viruses examined were susceptible to oseltamivir and zanamivir and resistant to adamantane antiviral medications.


CONCLUSIONS
In a large outbreak of variant influenza, the majority of infected persons reported exposures, suggesting that swine contact at an agricultural fair was a risk for H3N2v infection. We identified limited person-to-person H3N2v virus transmission, but found no evidence of efficient or sustained person-to-person transmission. Fair managers and attendees should be aware of the risk of swine-to-human transmission of influenza viruses in these settings.
Influenza Division, National Center for Immunization and Respiratory Disease.
Michael A
MA
Jhung
Scott
S
Epperson
Matthew
M
Biggerstaff
Donna
D
Allen
Amanda
A
Balish
Nathelia
N
Barnes
Amanda
A
Beaudoin
Lashondra
L
Berman
Sally
S
Bidol
Lenee
L
Blanton
David
D
Blythe
Lynnette
L
Brammer
Tiffany
T
D'Mello
Richard
R
Danila
William
W
Davis
Sietske
S
de Fijter
Mary
M
Diorio
Lizette O
LO
Durand
Shannon
S
Emery
Brian
B
Fowler
Rebecca
R
Garten
Yoran
Y
Grant
Adena
A
Greenbaum
Larisa
L
Gubareva
Fiona
F
Havers
Thomas
T
Haupt
Jennifer
J
House
Sherif
S
Ibrahim
Victoria
V
Jiang
Seema
S
Jain
Daniel
D
Jernigan
James
J
Kazmierczak
Alexander
A
Klimov
Stephen
S
Lindstrom
Allison
A
Longenberger
Paul
P
Lucas
Ruth
R
Lynfield
Meredith
M
McMorrow
Maria
M
Moll
Craig
C
Morin
Stephen
S
Ostroff
Shannon L
SL
Page
Sarah Y
SY
Park
Susan
S
Peters
Celia
C
Quinn
Carrie
C
Reed
Shawn
S
Richards
Joni
J
Scheftel
Owen
O
Simwale
Bo
B
Shu
Kenneth
K
Soyemi
Jill
J
Stauffer
Craig
C
Steffens
Su
S
Su
Lauren
L
Torso
Timothy M
TM
Uyeki
Sara
S
Vetter
Julie
J
Villanueva
Karen K
KK
Wong
Michael
M
Shaw
Joseph S
JS
Bresee
Nancy
N
Cox
Lyn
L
Finelli
D000293:Adolescent; D000328:Adult; D000368:Aged; D002648:Child; D002675:Child, Preschool; D016358:Contact Tracing; D004196:Disease Outbreaks; D005260:Female; D006760:Hospitalization; D006801:Humans; D007223:Infant; D053122:Influenza A Virus, H3N2 Subtype / Q000302:isolation & purification*; D007251:Influenza, Human / Q000453:epidemiology* / Q000635:transmission / Q000821:virology*; D008297:Male; D008875:Middle Aged; D014481:United States / Q000453:epidemiology; D055815:Young Adult
influenza; outbreak; pandemic; variant influenza