Hemagglutination inhibitation titers.

*Antisera against the common H9 serotypes. The abbreviations are the isolate number of the antigen against which the sera were made. All are chicken antisera except α-A/Chicken/Hong Kong/G9/97 and α-A/Hong Kong/1073/99, which are goat or sheep hyperimmune antisera, respectively. Homologous sera are in boldface. Titers are expressed as the reciprocal of the last dilution that completely inhibited hemagglutination of 0.5% chicken erythrocytes.†Isolates reported in Aamir et al. (2007).