Number and percent of live poultry market workers and non-poultry worker controls whose serum tested positive for neutralizing antibody against H9 viruses by age.^a

a

Individuals were stratified by age to control for prior exposure to human influenza viruses. In 2001, individuals born in or before 1968 were ≥33 years of age and may have experienced infection with H2N2 and H3N2 viruses while individuals born after 1968 were <33 years of age would not have been exposed to H2N2 viruses.

b

Non-adsorbed sera were considered to be preliminarily positive for antibody to an H9 virus if a titer of ≥40 was obtained in two independent assays and tested positive by Western immunoblotting for reactivity with purified recombinant H9 HA.

c

Sera were adsorbed with human influenza viruses depending on the age of the individual. Sera from individuals <33 years of age were adsorbed with the contemporary human H3N2 virus A/Panama/2007/99; sera from individuals ≥33 years of age were adsorbed with the H2N7 reassortant virus.

d

H9N7 virus is a reassortant possessing the hemagglutinin (HA) of A/Chicken/Hong Kong/G9/1997 virus (H9N2) and the neuraminidase (NA) from A/Equine/Prague/1/56 (H7N7) virus.

*

p = 0.7710 Fischer's Exact Text.

**

p = 1.000 Fischer's Exact Text.