title: Ongoing transmission of avian influenza A viruses in Hong Kong despite very comprehensive poultry control measures: A prospective seroepidemiology study.
abstract: OBJECTIVE
  Stringent measures have been implemented in Hong Kong to prevent human infections due to avian influenza viruses (AIVs). Here, we report the seroprevalence of AIVs among high risk population.
  
  
  METHODS
  In this prospective study, blood samples were collected in October and November 2013 and in July 2014 from workers at live poultry market (LPM) and pig/cattle slaughterhouse (SH) in Hong Kong. Serum antibody titers against A(H5N1), A(H7N9) and A(H9N2) were determined.
  
  
  RESULTS
  When an hemagglutination inhibition (HI) titer of 40 was used as the cutoff, the A(H5N1) seropositive rate among LPM workers increased from 0% in 2013 to 37.8% in 2014 (P < 0.001) and the A(H9N2) seropositive rate increased from 10% to 55.6% (P < 0.001). There was no significant increase in A(H7N9) seropositive rate for LPM workers irrespective of cutoff titer. For SH workers, there was no significant increase in HI titer for any AIVs. Significantly more LPM workers had a ≥4-fold increase in A(H5N1) HI titer from 2013 to 2014 than SH workers (60% vs 8.3%, P = 0.020).
  
  
  CONCLUSIONS
  There was a significant increase of serum A(H5N1) and A(H9N2) HI titers among Hong Kong LPM workers between 2013 and 2014. Although we cannot exclude some degree of antibody cross-reactivity with other influenza viruses, our results suggest the occurrence of subclinical AIV infections in this population.
authors.affiliation: State Key Laboratory for Emerging Infectious Diseases, The University of Hong Kong, Hong Kong, China; Carol Yu Centre for Infection, The University of Hong Kong, Hong Kong, China; Research Centre of Infection and Immunology, The University of Hong Kong, Hong Kong, China; Department of Microbiology, The University of Hong Kong, Hong Kong, China.
authors.forename: Kelvin K W
authors.initials: KK
authors.lastname: To
authors.affiliation: Carol Yu Centre for Infection, The University of Hong Kong, Hong Kong, China; Research Centre of Infection and Immunology, The University of Hong Kong, Hong Kong, China; Department of Medicine, The University of Hong Kong, Hong Kong, China.
authors.forename: Ivan F N
authors.initials: IF
authors.lastname: Hung
authors.affiliation: Department of Microbiology, The University of Hong Kong, Hong Kong, China.
authors.forename: Yin-Ming
authors.initials: YM
authors.lastname: Lui
authors.affiliation: Department of Microbiology, The University of Hong Kong, Hong Kong, China.
authors.forename: Florence K Y
authors.initials: FK
authors.lastname: Mok
authors.affiliation: Department of Microbiology, The University of Hong Kong, Hong Kong, China.
authors.forename: Andy S F
authors.initials: AS
authors.lastname: Chan
authors.affiliation: Department of Microbiology, The University of Hong Kong, Hong Kong, China.
authors.forename: Patrick T W
authors.initials: PT
authors.lastname: Li
authors.affiliation: Department of Microbiology, The University of Hong Kong, Hong Kong, China.
authors.forename: Tin-Lun
authors.initials: TL
authors.lastname: Wong
authors.affiliation: Department of Microbiology, The University of Hong Kong, Hong Kong, China.
authors.forename: Deborah T Y
authors.initials: DT
authors.lastname: Ho
authors.affiliation: State Key Laboratory for Emerging Infectious Diseases, The University of Hong Kong, Hong Kong, China; Carol Yu Centre for Infection, The University of Hong Kong, Hong Kong, China; Research Centre of Infection and Immunology, The University of Hong Kong, Hong Kong, China; Department of Microbiology, The University of Hong Kong, Hong Kong, China.
authors.forename: Jasper F W
authors.initials: JF
authors.lastname: Chan
authors.affiliation: State Key Laboratory for Emerging Infectious Diseases, The University of Hong Kong, Hong Kong, China; Carol Yu Centre for Infection, The University of Hong Kong, Hong Kong, China; Research Centre of Infection and Immunology, The University of Hong Kong, Hong Kong, China; Department of Microbiology, The University of Hong Kong, Hong Kong, China.
authors.forename: Kwok-Hung
authors.initials: KH
authors.lastname: Chan
authors.affiliation: State Key Laboratory for Emerging Infectious Diseases, The University of Hong Kong, Hong Kong, China; Carol Yu Centre for Infection, The University of Hong Kong, Hong Kong, China; Research Centre of Infection and Immunology, The University of Hong Kong, Hong Kong, China; Department of Microbiology, The University of Hong Kong, Hong Kong, China. Electronic address: kyyuen@hku.hk.
authors.forename: Kwok-Yung
authors.initials: KY
authors.lastname: Yuen
mesh_terms: D000818:Animals; D000914:Antibodies, Viral / Q000097:blood; D002417:Cattle; D003140:Communicable Disease Control / Q000379:methods*; D018562:Disease Transmission, Infectious; D005260:Female; D006385:Hemagglutination Inhibition Tests; D006723:Hong Kong / Q000453:epidemiology; D006801:Humans; D053124:Influenza A Virus, H5N1 Subtype / Q000276:immunology; D064766:Influenza A Virus, H7N9 Subtype / Q000276:immunology; D053127:Influenza A Virus, H9N2 Subtype / Q000276:immunology; D005585:Influenza in Birds / Q000453:epidemiology* / Q000517:prevention & control / Q000635:transmission; D007251:Influenza, Human / Q000453:epidemiology* / Q000517:prevention & control; D008297:Male; D008875:Middle Aged; D016273:Occupational Exposure; D011200:Poultry; D011446:Prospective Studies; D016036:Seroepidemiologic Studies; D015047:Zoonoses / Q000453:epidemiology* / Q000517:prevention & control
chemical_list: D000914:Antibodies, Viral
keywords: Avian influenza; Epidemiology; H5N1; H7N9; H9N2; Hong Kong; Seroprevalence