Triple-reassortant swine influenza A (H1) in humans in the United States, 2005-2009.
BACKGROUND
Triple-reassortant swine influenza A (H1) viruses--containing genes from avian, human, and swine influenza viruses--emerged and became enzootic among pig herds in North America during the late 1990s.


METHODS
We report the clinical features of the first 11 sporadic cases of infection of humans with triple-reassortant swine influenza A (H1) viruses reported to the Centers for Disease Control and Prevention, occurring from December 2005 through February 2009, until just before the current epidemic of swine-origin influenza A (H1N1) among humans. These data were obtained from routine national influenza surveillance reports and from joint case investigations by public and animal health agencies.


RESULTS
The median age of the 11 patients was 10 years (range, 16 months to 48 years), and 4 had underlying health conditions. Nine of the patients had had exposure to pigs, five through direct contact and four through visits to a location where pigs were present but without contact. In another patient, human-to-human transmission was suspected. The range of the incubation period, from the last known exposure to the onset of symptoms, was 3 to 9 days. Among the 10 patients with known clinical symptoms, symptoms included fever (in 90%), cough (in 100%), headache (in 60%), and diarrhea (in 30%). Complete blood counts were available for four patients, revealing leukopenia in two, lymphopenia in one, and thrombocytopenia in another. Four patients were hospitalized, two of whom underwent invasive mechanical ventilation. Four patients received oseltamivir, and all 11 recovered from their illness.


CONCLUSIONS
From December 2005 until just before the current human epidemic of swine-origin influenza viruses, there was sporadic infection with triple-reassortant swine influenza A (H1) viruses in persons with exposure to pigs in the United States. Although all the patients recovered, severe illness of the lower respiratory tract and unusual influenza signs such as diarrhea were observed in some patients, including those who had been previously healthy.
Shinde
Vivek
V
Influenza Division, Centers for Disease Control and Prevention, Atlanta, GA 30333, USA.
Bridges
Carolyn B
CB
Uyeki
Timothy M
TM
Shu
Bo
B
Balish
Amanda
A
Xu
Xiyan
X
Lindstrom
Stephen
S
Gubareva
Larisa V
LV
Deyde
Varough
V
Garten
Rebecca J
RJ
Harris
Meghan
M
Gerber
Susan
S
Vagasky
Susan
S
Smith
Forrest
F
Pascoe
Neal
N
Martin
Karen
K
Dufficy
Deborah
D
Ritger
Kathy
K
Conover
Craig
C
Quinlisk
Patricia
P
Klimov
Alexander
A
Bresee
Joseph S
JS
Finelli
Lyn
L
D000293:Adolescent; D000328:Adult; D017677:Age Distribution; D000818:Animals; D001717:Birds; D001772:Blood Cell Count; D002648:Child; D002675:Child, Preschool; D021821:Communicable Diseases, Emerging / Q000453:epidemiology* / Q000821:virology; D004196:Disease Outbreaks / Q000706:statistics & numerical data*; D005260:Female; D005838:Genotype; D006388:Hemagglutinins / Q000235:genetics; D006801:Humans; D007223:Infant; D053118:Influenza A Virus, H1N1 Subtype / Q000235:genetics*; D007251:Influenza, Human / Q000453:epidemiology / Q000635:transmission / Q000821:virology*; D008297:Male; D008875:Middle Aged; D009976:Orthomyxoviridae Infections / Q000635:transmission / Q000662:veterinary / Q000821:virology; D010802:Phylogeny; D011159:Population Surveillance; D016865:Reassortant Viruses / Q000235:genetics*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017422:Sequence Analysis, DNA; D034421:Sus scrofa; D014481:United States / Q000453:epidemiology
D006388:Hemagglutinins