Human H5N2 avian influenza infection in Japan and the factors associated with high H5N2-neutralizing antibody titer.
BACKGROUND
H5N2 avian influenza virus infection of humans has not been reported thus far. The first H5N2 avian influenza infection of poultry in Japan occurred in Ibaraki.


METHODS
The subjects were workers at 35 chicken farms in Ibaraki Prefecture, where the H5N2 virus or antibody was isolated from chickens. None of the subjects exhibited influenza symptoms. The H5N2-neutralizing antibody titers of the first and second paired sera samples were compared. To investigate the possible factors for this increase, the H5N2-neutralizing antibody titer (1:40 or more) was calculated for the second samples. A logistic regression analysis was performed to examine the association of these factors with H5N2-neutralizing antibody positivity.


RESULTS
We performed Wilcoxon matched-pairs signed-ranked test on data collected from 257 subjects, and determined that the H5N2 antibody titers of the second paired sera samples were significantly higher than those of the first samples (P < 0.001). The H5N2 antibody titers of paired sera of 13 subjects without a history of seasonal influenza vaccination within the previous 12 months increased 4-fold or more. The percentage of antibody positivity was 32% for subjects with a history of seasonal influenza vaccination (28% of all subjects) and 13% for those without a history of the same. The adjusted odds ratio of H5N2-neutralizing antibody positivity was 4.6 (95% confidence interval: 1.6-13.7) for those aged over 40 and 3.1 (95% confidence interval: 1.6-6.1) for those with a history of seasonal influenza vaccination within the previous 12 months.


CONCLUSIONS
The results suggest that this may have been the first avian influenza H5N2 infection of poultry to affect humans. A history of seasonal influenza vaccination might be associated with H5N2-neutralizing antibody positivity.
Ogata
Tsuyoshi
T
Chikusei Health Center, Ibaraki Prefectural Government, Ibaraki, Japan. t.ogata@pref.ibaraki.lg.jp
Yamazaki
Yoshinao
Y
Okabe
Nobuhiko
N
Nakamura
Yosikazu
Y
Tashiro
Masato
M
Nagata
Noriko
N
Itamura
Shigeyuki
S
Yasui
Yoshinori
Y
Nakashima
Kazutoshi
K
Doi
Mikio
M
Izumi
Youko
Y
Fujieda
Takashi
T
Yamato
Shin'ichi
S
Kawada
Yuichi
Y
D000818:Animals; D000914:Antibodies, Viral / Q000032:analysis*; D002645:Chickens; D004196:Disease Outbreaks / Q000517:prevention & control / Q000662:veterinary*; D018562:Disease Transmission, Infectious; D004784:Environmental Monitoring / Q000706:statistics & numerical data*; D062665:Epidemiological Monitoring; D004866:Equipment Contamination / Q000517:prevention & control; D006801:Humans; D006920:Hygiene; D007110:Immunity, Active; D053125:Influenza A Virus, H5N2 Subtype / Q000276:immunology*; D005585:Influenza in Birds / Q000453:epidemiology* / Q000635:transmission*; D007564:Japan / Q000453:epidemiology; D016273:Occupational Exposure; D012044:Regression Analysis; D018570:Risk Assessment
D000914:Antibodies, Viral